Nail Technology Terminology

Glossary of Nail Technology Terminology

The terminology used in nail technology can be very confusing at times. Many terms are unclear, ambivalent, or downright backward and upside down! Sometimes it can be hard for new techs (and even veterans) to be sure what is being discussed or described when watching a video, taking a class, reading manufacturer instructions, or simply chatting with a client or fellow professional.

This list contains standardized definitions of many commonly used terms, procedures, products, chemicals, MSDS/chemical terms, and nail anatomy as used regarding natural nails and nail enhancements.

This glossary will likely be a perpetual project in process and we welcome any discussions of alternate definitions (we’re not perfect, mistakes can happen!), and requests for additional terms to be added. Direct email regarding omissions or corrections to:

ABS Plastic

Acrylonitrile-butadiene-styrene monomers, a co-polymer used in the manufacture of most plastic nail tips.


A substance added or applied that takes part in a chemical reaction, meaning that it becomes part of the finished product. See "catalyst" also.


Having a pH of less than 7. Vinegar and lemon juice are acids. See also "pH".

Acid Primer

Acrylic acid primer: usually refers to methacrylic acid type primers (MAP) that promote adhesion between thenatural nail and enhancement product.


Solvent used to break down nail polish and acrylics. A chemical in the ketone family. Acetone is neither better or worse than non-acetone polish removers. Non-acetone polish removers are made from MEK – methyl ethyl ketone, also a member of the ketone family.


Generally refers to two-part liquid monomer and powdered polymer nail systems.

Acute Effects

Adverse health effects caused by sudden or short-term exposure. Refers to single or multiple exposures within one 24-hour period or less. See also “chronic effects."


Generally found in UV gel nail products.


A chemical substance that causes two surfaces to stick together. The most common nail adhesive is cyanoacrylate.


A chemical used to destroy bacteria, fungus, and viruses on human skin. The process of disinfection is used for surfaces or implements.


The art of applying nail decorations with an airbrush gun.

Allergic Reaction

An adverse reaction in the body usually characterized by skin redness, itching, blisters and localized swelling. Misuse of nail products can lead to allergic reactions.


Hardened and cured coating that results from a precise mix ratio of liquid monomer and powdered polymer. Most acrylic monomers are made primarily from Ethyl Methacrylate (EMA). The polymers contain approximately 70% EMA and 30% MMA (Methyl Methacrylate), and a very small percentage of initiator, such as Benzoyl Peroxide. Note: MMA is not harmful when it is a solid (powder/polymer), but is considered harmful in its’ liquid form (monomer). Nail techs should avoid acrylic systems with MMA monomer.

Acrylic Brush

Usually a natural hair bristle brush used to apply acrylic nails. They come in various sizes, shapes, and styles.

American Manicure

Usually describes a variation on the French Manicure, where a more natural white is used on the tip (vs. a brighter white in FM), and the polish used on the bed is more sheer (vs. more opaque in FM).


AKA: Fill, fill-in, touch-up, maintenance, etc. In the early days of the nail industry, a back-fill was considered a more thorough fill process than normal fills. Whereby arches were moved back, and the entire nail was balanced. In today’s more technical and advanced standards, every fill appt. is considered to be a complete back-fill service. Also, some salons use the term back-fill to differentiate a fill on pink and whites (back-filling the white free-edge), and the term fill to mean a regular fill on non-P&W’s.


A single cell organism. Some bacteria are capable of causing disease. Bacterial spores are a dormant state of some bacteria. Viruses are a large group of infective agents that reproduce in living cells.


Also known as alkali or alkaline, having a pH value of greater than 7 (on the pH scale of 0-14, with 7 being neutral). Acetone is a base with a pH of about 9 or 10. Baking soda is also a base. Microorganisms are killed by both high and low pH values.

Benzoyl Peroxide

A heat-sensitive initiator used in acrylic nails.

Boiling Point

Part of the Physical Data section of the MSDS. The lower the boiling point, the greater the flammability risks.

Breathing Zone

The two-foot area around your head, from which all your breathing air is drawn; especially relevant when working with Volatile Organic Compounds (VOC’s). VOC’s are found in many nail products. Nail techs should protect their breathing zone when working with nail products.


How likely something is to break under force. Example: Glass is strong (not easily dented or scratched), but it is brittle (will break if you drop it for instance).

CAS Number

Chemical Abstract Service identification number. Like a chemical fingerprint. Every chemical has one unique number assigned to it. This information can be vital should you ever need to contact poison control; rather than trying to pronounce the names of the chemicals, you can simply give the CAS# as listed on the MSDS. This is yet another reason why salons should keep MSDS on all the products they use.


Differs from an accelerator in that a catalyst will not become part of the finished product. A catalyst will help start a chemical reaction (usually so that the reaction will happen faster), but it will not take part in the chemical reaction.


Everything we can see and touch, except for light and electricity. All substances are either pure chemicals or combinations of pure chemicals. All matter is composed of chemicals.


In nails, refers to a style of French Manicure. Instead of following the natural smile line on the tip area with white polish (or colored polish, or airbrush), an inverted “V” shape is used.

Colored Acrylics and Gels

Pre-colored acrylic or gel product that allows for the building of nails with color built-in to the structure of the nail. Also great for nail art.


Contact with or addition of one substance that makes another substance impure.


Polymers made of two or more different types of monomers. ABS plastic used in nail tips is a co-polymer.

Corrosive or Caustic

Substances capable of causing rapid damage to human skin. Having a very high (base) or low (acid) pH, both are equally damaging and dangerous.

Covalent bond

Thejoining of two atoms when the two share a pair of electrons.

Thejoining of two atoms when the two share a pair of electrons.

A chemical bond between polymer chains. Cross-linking occurs when individual polymer chains are linked together by covalent bonds to form one giant molecule.


The formation of very small crystals in uncured acrylic resulting from cold temperatures or drafts. The cause is liquid monomer freezing into a solid during application, thus preventing it from correctly polymerizing around the powdered polymer.


The complete hardening of a nail coating that goes beyond the “drying” stage.

Curing Agent

Substance (catalyst or accelerator) used to “harden” (cure) a product. Every type of nail product utilizes some form of curing agent (heat to evaporate solvents during polymerization of acrylics or photo-initiators in gels). Even water can be a curing agent; exposure to water in the air (humidity) is responsible for causing nail adhesives to dry, hence why they need to be kept closed.


Nail adhesive or resin ingredient used in nail tip application and wraps.


A layer of translucent or colorless skin that is shed from the underside of the proximal nail fold.


The highest level of decontamination is sterilization, next is disinfection, and least effective is sanitation.


To dissolve the fat from human skin. Many solvents are defatting by nature and can cause drying and cracking of the skin.


To dehydrate the nail, means to remove moisture from the surface, which will improve adhesion and help to prevent growth of yeast, bacteria and fungi. Dehydrators are substances capable of absorbing water from the natural nail.


The peeling apart of two previously adhered or layered surfaces. Natural nails can de-laminate due to a lack of natural oil and moisture in the nail plate layers; this is most often referred to as peeling nails. In regards to acrylic nails or other nail enhancement systems, it describes lifting of the enhancement (acrylic) from the natural nail.


The bottom layer of skin (which is under the epidermis). The nail moves with the epidermis as it grows on the dermis.


A procedure used to control microorganisms on non-living surfaces such as: instruments, implements and surfaces. Please see the Sanitation section of this site for more information on disinfection, sanitation, and sterilization.

Distal Edge of Nail

Distal means far. In nail technology, it is used to describe the part of the nail farthest away from the cuticle area.


Nail polishes with a higher level of film-formers are generally distinguished as enamels.


The upper most layer of skin. It is attached to the bottom of the nail plate and is ridged with tiny 'rails' that run in the same direction as the dermis grooves. The effect is much like a train riding on its tracks as it moves forward.


The extension of the proximal (near) nail fold at the base of the nail body that partly overlaps the lunula. This is live tissue and should never be cut or nipped.


A small specific portion of a structure of a molecule. All nail coating polymers - except for polishes - contain ester


The term “etch” is a misnomer in the field of nail technology. The true meaning of the word is “ the process of making a design on a hard surface by corroding its’ surface with acid”. This term is often misused to describe the filing process used to remove the surface shine from natural nails in preparation for a nail enhancement service. The correct terminology is to “remove surface shine” with a high-grit file or buffer. “Etching” on the other hand, is an over-aggressive and damaging method of nail prep, usually accomplished by using a heavy hand and a rough file (low grit such as 80 or 100). This not only removes the surface shine, but also disrupts the nail plate layers and “roughs up” the nail. Today's products do no use this damaging method to ensure adhesion, as it can weaken the bond between nail and acrylic, leading to lifting.

Ethyl Methacrylate (EMA)

Ethyl Methacrylate is the most widely used monomer in 2-part systems used to create artificial nail enhancements (monomer/polymer, AKA liquid and powder). EMA can be safely soaked from nails for complete removal. EMA is considered a 'flexible' monomer.


Heat releasing reaction that occurs when two monomers join. All nail enhancement products release heat. Sometimes this heat can be felt – especially when curing U-V gels, or when using adhesive dryers or wrap accelerator sprays, and occasionally with liquid powder acrylic systems.


To maintain a set of nails after the full-set. See “back-fill”.

Film Formers

Polymers that form hard smooth surfaces after the solvents evaporate. Used in nail polish and hair spray.

Flash Point

The temperature at which a substance gives off a sufficient amount of vapors to form an ignitable mixture with air. Products with a low flash point (below 100° F) should not be used in the presence of (or near) fire, flame, sparks or high heat (such as a lit cigarette, candle, or even in an automobile trunk). The flash point of a product can be found in the MSDS. Note: The lower the flash point, the more potentially dangerous the product.

Flammability/Explosive Limits

Refers to the LEL (lower explosive limit) and UEL (upper explosive limit). The greater the range between these two numbers (as found on the MSDS), the greater the hazard (the easier it can catch fire).


How much a substance will bend under force.

Free Radicals

Very excited molecules which cause many kinds of chemical reactions, including polymerization of acrylic nails.

French Manicure

A type of nail polishing procedure, whereby the natural free-edge of the nail is painted white, and the nail bed is painted pink, beige, or clear, to mimic a healthy looking natural nail. Sometimes the moons (lunulas) are painted in as well.


Very small, fine, solid particles suspended in air, such as smoke. Nail products do not produce fumes; they produce vapors. See “vapors”.


Microscopic and multi-celled plant organisms, such as mold, dermatophytes, and yeast. Only 2 members of this family can form colonies (infect) in or under the natural nail: Candida Albicans (a yeast), and Trichophyton Rubrum (a dermatophyte that feeds on keratin and other dead tissue). Molds do NOT infect nails. Many times green bacterial infections are mistakenly called a mold or fungus. Since fungi cannot make their own food, they are considered parasites, and feed on organic matter (such as the keratin protein in nails. They multiply rapidly. They can go dormant (hibernate) by protecting itself with a hard spore shell, and then reappear 6 months or many years later to re-infect their host.

Gel (Gel Nails)

Often referred to as not being “acrylic”, when in fact they are based on both the methacrylate and the acrylate family, and are indeed acrylic. Gels are made by pre-joining monomers into short chains called oligomers. Oligomers are single chains that are several thousand monomers long. These oligomers are then cured (hardened to create rigid surface coatings) by exposure to ultra violet light. (No-lite gels are simply a thickened cyanoacrylate in a “gel type” form, and should not be confused with U-V light cured gel nail; technology.) Gel also refers to a high viscosity (thick) liquid, as in “gel type” nail adhesives.

Gel (alternate chemical definition)

A cross-linked polymer that has absorbed a large amount of solvent. Cross-linked polymers usually swell a good deal when they absorb solvents.

Gel Cleanser

A solvent (usually alcohol and/or acetone based) used to remove the stick/tacky dispersion layer that is left after gels cure in the U-V light source. Once it is removed, a very smooth and shiny surface will be revealed.

Gel Light

An ultra violet light source (UVA) used to cure gel nails. They come in many different shapes, sizes, styles, and most importantly bulb styles. See the “Gel Nails” educational section of this site for more information on gel lights.


The term glue is often used incorrectly to describe nail adhesive. True glues are protein based, not cyanoacrylate based as those in the nail industry. The correct terminology to use is nail adhesive.


A numerical measure of the coarseness of a file or buffer; these are the same numbers used to define sandpaper. Low numbers are the most coarse (such as 80-100 grit files), and the highest numbers are the least coarse (or softest). High-shine buffers (for both nails and autos) can reach the thousands. Medium is generally 120-240. Soft is above 240, and super-soft buffers or shiners are above 1,000 plus. This is a general guideline only however, as the type of material a file is made out of can affect the relative “feel” of coarseness or softness. (Such as emery, diamond, plastic, zebra, etc.) The best way to know is to first a) follow the manufacturers recommendations (and files) for the product, and b) try other and comparable files out at shows, or individually purchase an assortment from your supplier to try.


An accelerator or catalyst. A substance that promotes, speeds up, or controls the curing/drying/hardening process during the chemical reaction that takes place during the change from one physical state to another, such as liquid to solid in acrylic or gel nails.


A measure of how easily a substance is scratched or dented. A substance can be very hard (such as glass), yet be brittle, and thus able to be broken easily.

Hazardous Ingredient

Any substance that may be capable of causing physical or health related injury to an exposed individual. MSDS contain info on potentially hazardous ingredients in salon products. Following proper handling and product safety measures can reduce hazards. See “Safety In The Salon” within the education section of this website for more info on the handling of hazardous ingredients.


The portion of the epidermis (skin) under the free edge of the nail that forms a seal to protect the nail bed. Some clients may have an overgrown hyponychium that attaches to the underside of the free-edge of the nail and continues to grow forward with it. This is live tissue and must not be cut. If a clients’ hyponychium becomes painful or problematic, refer her to her doctor.


This chemical substance makes up the nail plate. Keratin in a protein. Proteins are the building blocks of life!


A product made by bonding together two or more layers of materials, or to unite layers of material together with an adhesive.

Lateral Nail Fold

The soft tissue at and around the sides of the natural nail.

Linear Polymer

Chains of polymers that are not cross-linked. These polymers have less strength and are more easily dissolved in solvents (such as acetone or water) than cross-linked. Cyanoacrylate (nail adhesive) is an example of a linear polymer.

Local Exhaust

Ventilation system that collects vapors and dust right at their source. Most nail products’ MSDS specifically specify the need for local exhaust. General or mechanical exhaust is different in that they draw air toward a general circulation system in the room (such as an exhaust fan or room air cleaner). While general exhaust is helpful, it simply is not enough proper ventilation to protect the nail tech’s health over the life of her career. Please see the “Safety” section in this website for more information on exhaust systems, as well as tips for designing and building an efficient local exhaust. Note: Vented nail tables are a step in the right direction toward local exhaust, however, unless they are vented outside, or have their filters cleaned/changed daily, (not to mention that the vent should not be covered with a towel), they will not be strong enough to trap airborne dust and vapors before they pass through your breathing zone.


Also known as half moon, the lunula is located at the base of the nail where the matrix and the connective tissue of the nail meet. The area under the lunula is the front of the matrix. The light color of the lunula may be due to the reflection of light on this soft/unhardened nail area. It has long been held that the larger and whiter the moons (lunula), the healthier the natural nail.

Material Safety Data Sheets (MSDS)

Chemical information sheets. They contain safety precautions on each potentially hazardous product in the salon. It is an OSHA regulation (state and federal laws) for all salons to have MSDS on premises for all products containing potentially hazardous chemicals. Acquire them from nail manufacturers or distributors, and collect into a 3-ring binder displayed prominently in your salon. Many MSDS are now also found online for easy download.


The part of the nail bed that extends beneath the nail root and contains nerves, lymph and blood vessels. The matrix produces the nail and its cells undergo a reproducing and hardening process. The matrix will continue to grow as long as it receives nutrition and remains in a healthy condition.

Mechanical Exhaust

Draws air toward a general circulation system in the room (such as an exhaust fan in the wall). While general exhaust is helpful, it simply is not enough to protect the nail tech’s health over the life of her career. Please see the “Safety” section in this website for more information on exhaust systems. See also “Local Exhaust” above and “Ventilation” below.

Mesh Size

Refers to the particle size of acrylic powders. Think of the mesh as a sifter; the more holes there are in a sifter, the smaller each hole will be. The fewer holes there are in this same sized sifter, the larger the holes will be. So, higher mesh size, means smaller sifting holes, means smaller particles. Lower equal bigger particles. Smaller particle size (thus larger mesh size number) is better! Larger particles (smaller mesh sizing) produce acrylics that are coarser (less smooth), and harder to file. Why is this so? Because the acrylic powder does not become part of the actual acrylic nail polymer. Instead, powder (previously polymerized monomer) is ground up and used only as a base (a filler), or scaffolding for the liquid monomer to polymerize on and around. It is the monomer that is polymerizing together around the powder particles. The powder does not mix with the liquid monomer. The powder is inert. Thus, why it is better to have smaller acrylic polymer powder particles than larger ones. For more info on the hardening and curing process of acrylics (and gels) see the section in “Gel Nails” on “How Gels Work”.


One of the many families of acrylics.

Methyl Methacrylate (MMA)

An acrylic monomer banned by the FDA in 1978 for use in nail products because of the serious health risks. See “MMA” below.


Bacteria, viruses, fungus, and protozoa.


A white or grayish coating formed by fungi on plant leaves, cloth, paper, etc. Mildew will not and cannot infect human nails.


Fine liquid particles of various sizes suspended in air; produced by spraying air (or other propellant) through a liquid to disperse it into the air..

Mix Ratio

Relation in degree or number between two things. Ratio of liquid to powder in acrylic systems. Such as 1:1 (even mix ratio), or 1:2 (a dry mix of twice as much powder as liquid), or 2:1 ( a wet mix of twice as much liquid as powder).

MMA (Methyl Methacrylate)

MMA in its liquid form has been banned for use in the nail industry due to the severity of allergic reaction and damage to the natural nail plate. It adheres so tightly to the nail plate that it can literally rip the nail plate from the nail bed under pressure from a blow or trauma to the nail. MMA is so hard that it can take hours to soak off in pure acetone (not a safe practice) -- so it must be filed from the nail plate with a heavy abrasive or electric file.


A type of fungous growth that forms on the surface of organic matter. Mold is not a human pathogen, thus it cannot infect human nails.


The liquid part of acrylic nail systems. Individual, reactive chemical units that may be linked together to form a polymer. A small molecule that may react chemically to link with other molecules of the same type to form a larger molecule called a polymer.

Nail Bed

Underneath the nail. The portion of skin that the nail plate rests on. It contains blood vessels that supply nutrients to the fingertip.

Nail Plate

The hard keratin (protein) coating that protects the fingertip and underlying tissue. What we commonly refer to as our “nails”.

Nail Root

is at the base of the nail and is embedded underneath the skin. It originates from an actively growing tissue known as the matrix.

NFPA Hazard Classification

National Fire Protection Agency rating for chemicals in four classifications: Health, Flammability, Reactivity, and Other. Ratings are from zero to four in each area. Zero means no danger, while a rating of 4 means extreme danger potential.


A tool used in a nail salon for a variety of purposes, including cuticle care, toenail clipping, and the nipping of acrylics. For help in choosing nippers, see “Metal Implements” in “Nail Tech 101” for more info on the various types of construction (jaws, joints, springs, sizes) and their uses.

Non-acid Primer

A misnomer, as all primers are acidic to some degree or another. However, the term is commonly used to refer to any primer that does not use methacrylic acid (MAP). See also “Methacrylic Acid” above.

Odorless Acrylics

Acrylic liquids that are not as easily detected by the human sense of smell (as compared to regular acrylics). Odorless does not mean that they have a slower evaporation rate or are any safer than odoured products.


Monomers that have been pre-linked into short chains. A polymer whose molecular weight is too low to really be considered a polymer. Oligomers have molecular weights in the hundreds, but polymers have molecular weights in the thousands or higher. UV gels are oligomers. Uncured gels are oligomers.


Any substance that contains the element carbon. Nearly half the substances in the world contain carbon, and almost all nail products contain carbon. Organic does not mean safe. Petro-chemicals are carbon based, thus organic. Organic is simply a name used by scientists to distinguish one half of the stuff in this world (carbon-containing) from the other half (non-carbon based, thus inorganic).


Occupational Safety and Health Administration. Federal organization that works to ensure the safe working conditions for employees.


Chemical hazards caused from prolonged, repeated exposure beyond levels specified as safe by regulatory agencies, and as specified on the MSDS.


A microorganism that is capable of causing disease. Fungus is a pathogen.

Permissible Exposure Limit (PEL)

Parts per million (PPM) inhaled exposure limit of a substance. The amount of a substance in the air that can be breathed in a normal 40 hour week by most people without experiencing adverse health effects.

Permanent French Manicure (PFM)

See Pinks & Whites.


The acid and base scale of 0-14., it is the measure of hydrogen ions (H+) in water-based solution. A pH of 7 is neutral, less than 7 is acidic, greater than 7 is alkali (base). Pure water is 7, or skin is usually at around 5.5, (so slightly acidic). See also “Acid”, “Base”, and “Alkaline” above, and “pH and Primers” in the “Chemistry” section of this website.

Pink & Whites (P&W's)

The application of a white free-edge, and a pink (or clear or beige) nail bed, using colored acrylic or gel products, so that the French Manicure look is permanent and built-in to the structure of the nail. There is no need to apply nail polish.


An organic (carbon-based) polymer that displays “plastic” behavior: a solid substance that will bend, yield, or flow under stress or force.


Substance added to increase flexibility or workability of a product.

Plastic Tips

Used to extend the length of natural nails. They come in many styles, sizes, and even colors. See also “ABS Plastic” above and “Tips and Forms” in “Nail Tech 101” in the educational section of this website for more information.

Polish Remover

Solvents that dissolve nail polish, such as Acetone and Methyl-ethyl-ketone (MEK). See “Acetone” and “MEK” above.

Polish Thinner

Not the same as polish remover. Thinner is the same (or similar) chemical solvent found in the polish that evaporates as it dries (and evaporates from the open bottle thus causing the polish to thicken over time). Polish remover breaks down the chemicals in polish, hence why it is not a good thinner.


Chemical bonding of many smaller individual organic molecules into a larger structure. Our hair and nails are polymers of thousands of amino acids connected into chains that form keratin. Any of numerous natural and synthetic compounds of unusually high molecular weight consisting of repeated linked units, each a relatively light and simple molecule.


To cause a polymer to form. The process of forming a polymer. To unite two or more monomers to form a polymer.


A mixture of inorganic substances that have been fused together at extremely high temperatures. Not found in the nail industry, although sometimes the term has been used incorrectly for marketing purposes.


Containing pores or openings that will cause lower strength. Polymers used in the nail industry are classified as non-porous. However, the polymerized monomers are can still be porous for anywhere from 24-72 hours (and even up to 2-3 weeks) after application, during which time they are continuing to polymerize and completely cure. This is why some acrylics will stain from nail polish if they are painted immediately after application, but will not do so if polished as a later date.


Prep contains chemicals such as Ethyl and/or Butyl Acetate, Isopropyl Alcohol and other ingredients. Prep is a temporary dehydrator and deep cleanser that will remove the moisture and some of the oils from the nail plate layers. It will disinfect the nail plate, is a pH balancer, and aids in physical and chemical bonding. The effects of prep will last approximately 30 minutes before the nails oil and moisture are replaced by natural means. Prep is applied before primer.


Many primers are made from methacrylic acid (MAP) – considered traditional acid primer, while others are made from other proprietary (secret) chemicals (also acids, but much weaker than MAP). Although primers are caustic to skin, they are not caustic to the nail plate. Primers aid in product retention because one end of the molecular chain is attracted to molecules in the natural nail plate, and the other end is attracted to the monomer molecule. Primers act like double-sided sticky tape.

Proximal Nail Fold

Found at the base of the nail, it is often mistaken for the cuticle. The cuticle is actually shed from the underside of the proximal nail fold. 'Proximal' means "nearest attached end". The proximal nail fold acts like a gasket to seal off the matrix where the new nail plate is growing.


A reversal of the normal inward folding of the skin of the nail plate, or the lateral nail folds. This can be caused by trauma and by certain skin conditions such as lichen planus. A dermatologist can sometimes remove this excess tissue by using acid peels or surgery.

Pterygium Remover Tool

A misnomer for a tool used to remove excess dead tissue near the base of the nail. Especially useful during enhancement product application to ensure better adhesion.


Sanitize means to clean. Sanitation reduces the number of pathogens or bacteria on a surface. To sanitize something is to clean it. Nail techs must sanitize their implements before disinfecting them in liquid or sterilizing in an auto-clave. The spray-on cleaning solution you probably use to clean your table or in your home is a sanitizer.

Sector Sculpting

Structurally engineering the enhancement for proper balance. Usually refers to applying product in zones, for maximum performance in each area, such as: 1) Free-edge (C-Curve and strength) – usually a dryer mix. 2) Middle/body (arch placement and flexibility) – generally a wetter mix. 3) Cuticle area (lift resistance) – medium to wet.


A type of allergic reaction in which the affected person becomes increasingly sensitive to the allergy causing substance through repeated and prolonged contact.


A chemical that causes a substantial portion of exposed people or animals to develop an allergic reaction in normal tissue after repeated or prolonged exposure to a chemical.

Skin Absorption

The ability of certain chemicals to pass through the dermis and into the epidermis and then into the bloodstream.


Substances capable of dissolving other liquids or solids. Water is the “universal solvent”.

Specific Gravity

Info contained in the physical data section of the MSDS. Water =1. If specific gravity of a substance is greater than 1, then it will sink in water. If less than one, then it will float on water. See also “Vapor Density”, which is a similar measurement in relation to air.


Refers to the rigid epidermis that stays attached to the bottom of the nail plate until it grows beyond the free edge. This tissue is called the solehorn cuticle, and will eventually slough off by itself or is removed during a manicure. Solehorn is dead tissue, and should not be confused with the hyponychium, which is live tissue. Note: If a client can feel you cutting or pushing on any skin or tissue, then it is LIVE tissue and you must stop. However, it should be noted that this method is not foolproof, as some clients (particularly those with circulatory problems) may not feel your tissue manipulation, or may simply have a high pain tolerance, or be too embarrassed to admit any pain. Whenever in doubt, then don’t!


The process of turning from a liquid to a solid.


Used in nail art and especially stencil airbrushing.


Sterilization completely destroys all living organisms on solid, non-porous objects or surfaces. It is accomplished in an auto-clave at high temperature and high pressure. Sterilization of nail tech and salon tools is well above and beyond the sanitation requirements imposed by any state in the USA.


The ability of a substance to withstand breakage under force. The amount of stress an object can receive before it breaks. It is the combo of hardness and flexibility that determine strength. AKA toughness.


Surface active agent; improves the wetting absorption or flow of a liquid on a solid surface. Promotes slipperiness.


A measure of heat. Celsius (C) and Fahrenheit (F) conversions. To convert C degrees to F, do the following math: 1.8 times C degrees, plus 32 degrees, equals the degrees F. F to C: F minus 32, then divide by 1.8 = C.

Threshold Limit Value (TLV)

The amount of a substance that is deemed safe to breathe in. Basically the same as PEL (permissible exposure limits). TLV values are set by NIOSH (National Institute for Occupational Safety and Health), while OSHA sets PEL values. You will find one or the other on your MSDS, both are expressed as ppm (parts per million). See also “PEL”.


The ability of a liquid (usually a gel) to become thinner (lower viscosity) when stirred, but will return to original viscosity once the stirring is stopped.

The ability of a liquid (usually a gel) to become thinner (lower viscosity) when stirred, but will return to original viscosity once the stirring is stopped.

Tool used to cut plastic tips and nails in one motion. See picture in the section on "Metal Implements" in “Nail Tech 101”.

Tip Overlay

Any enhancement procedure that is done over plastic tips applied to the natural nails, rather than sculpted onto forms. See “Tips and Forms” in “Nail Tech 101” for more info.


A measure of the ability of a sample to absorb mechanical energy without breaking.

Trade Name

Like a brand name for consumer products. The chemical name would be like the generic name for a chemical. (Example: Jello-O is the brand name – or trade name in this example, while gelatin is the generic – or chemical name.)

Ultra-Violet (UV)

In nail technology, it refers to the long wave, UVA portion of the spectrum of light, which is 350-400nm (nano-meters). UVB rays are found at 250-275nm. Visible light is what we see as light and colors - from violet on the low end to red at the high end - it is just above UVA at 400-780nm.

UV Activated Topcoat

A top coat that penetrates the layers of polish below it and forms them into one solid layer. This layer is then chemically activated by an accelerator in the product that reacts with a UV light source, which speeds up the drying process of nail polish.

UV Light

Used to cure gel nails. See Ultra Violet above, and Gel Nails in educational sections for more info on gel lights.


The gas formed by the evaporation of liquids. Vapors are a health concern in salons. Vapors differ from fumes in that fumes contain solid particles suspended in the air (such as smoke). Nail products do not produce fumes, only vapors. See "fumes" also.

Vapor Density

The weight of chemical vapors compared to air, where air = 1. Greater than 1 means that it is heavier than air and will sink to the floor. Less than 1 means lighter than air and thus floats, or rises in the air. Vapors with high density (sinkers) are potentially more dangerous due to their ability to snake around the floor and find a source of flame or heat (such as hot water heater, cigarette, candle, etc), potentially igniting or exploding. Then, this vapor stream acts as a wick back to the origin and larger quantity of product in the container at your station, thus bringing the fire or explosion right onto your table top! Use this info to your advantage, and choose products with higher values when you have a choice.

Vapor Pressure

Refers to the vapors from evaporation over a liquid that could potentially ignite. The higher the number, the higher the evaporation rate, and the higher the flammability potential. This number is expressed in relation to 1=N-Butyl-Acetate (found in some prep products).


An exchange of air. To admit fresh air into a space in order to replace stale air. To collect dust and vapors from the area and discharge them from the building. Fans and other apparatus (air cleaners) that simply move the air or attempt to clean it without exhausting it outside do not provide ventilation. Note: Ventilation is not a replacement for local exhaust. See also “Mechanical Exhaust” and “Local Exhaust” above.


The measure of a liquid's ability to flow; which is closely related to the thinness or thickness of a liquid. This term is often used when discussing gel nail products. You will see this term used on the MSDS.


A measure of how quickly a liquid will form vapors at room temp. The more volatile (higher), the faster it will evaporate. Percentage (%) volatile refers to total evaporation potential; 100%=complete evaporation potential.


The ease with which a liquid spreads out to evenly cover a surface. Adhesives with better wetting have better adhesion. Streaking or beading can occur when liquids are repelled by a solid surface.


Discoloration of nail products caused by excessive exposure to light (such as tanning), excessive heat, or product contamination.