We see the brightly colored packaging in the aisles and watch the glossy ads of women with larger than life hair say you can have "75% more definition!" - but what is really going into your hair products? What makes a good gel different from a bad gel, and what is that thick, sticky liquid actually doing to your hair? Cosmetic chemist Tonya McKay breaks down the science of hair gels for us, so that what you spend your money on and put on your body is no secret to you.

Before you try one gel and make up your mind about gels as a whole, understand that the properties of hair gel are highly dependent upon its formulation (which ingredients are present and in what composition), your hair type, the other products in your hair, and the climate in which you live.

Why use styling products?

A styling product helps to provide shape and hold to a style by forming a film on the hair that creates physical bonds between adjacent strands, holding them in place. One method of achieving this is spot welding, where droplets of product are applied at critical junctures and hold the hair in place. Hair sprays perform in this manner and are useful in providing hold to hair.

Another method of creating hold is known as seam welding and involves the application of a product down the length of the hair shaft, which facilitates formation of physical bonds between adjacent hair strands. This creates the clumping effect so often desired by people with curly hair. These types of products also impart volume to the hair by increasing stiffness from the root, which lifts it away from the scalp. Gels, hair crèmes, waxes, and mousse provide hold via the seam welding mechanism. This type of hold is very susceptible to disruption due to physical manipulation, such as combing, touching and windy conditions.

So, what is a gel?

A gel is a colloidal dispersion of particles (ranging from nanometers to micrometers in size) in a liquid medium. The solid particles (oftentimes polymers) form a network throughout the liquid that swells and forms a jelly-like mass. Gels are comprised mostly of liquid, but can appear like solids when at rest. The application of force allows these gels to flow like liquids, which makes them useful for many applications, such as hair care products. In a hair gel, the product has a thick consistency in the bottle, but should come out of the container easily and spread evenly on the hair. As product is applied, the polymers deposit onto the surface of the hair and cause adjacent strands to be attracted to one another through capillary forces, creating clumps of curls.

As product is applied, the polymers deposit onto the surface of the hair and cause adjacent strands to be attracted to one another through capillary forces, creating clumps of curls.

Water evaporates slowly from the hair, and the polymers dry to form clear films. These solid films help maintain curl and shine until the bonds are either broken via mechanical forces (combing, touching, windy conditions) or until the product is removed by washing.

The composition of a hair gel:

water as the main ingredient

polymers for film-forming

emulsifiers for non-water soluble components

viscosity modifiers (thickeners, such as carbomer)

fragrance

preservatives

additives used to impart moisture, shine, and UV protection, and to modify the properties of the film that is formed

Modification of the film properties of hair gels is the subject of continuing research and development, both at the academic and corporate level. The reason for this lies in the fact that no current polymer or combination of polymers provides the perfect set of properties. Some polymers provide excellent hold, but are too brittle and can cause flaking or style disruption throughout the day. Others may get around the problem of being brittle, but may be susceptible to moisture and cause frizzy or dull hair in humid environments. Still others may provide all the desired hold and shine properties and be indifferent to climate, but may be difficult to remove with shampoo and can cause unattractive build up problems. It is also desirable that a hair gel maintain its properties over a broad range of temperatures, which can be another difficult obstacle to overcome.

Hold Agents

Some of the more frequently used polymer fixative agents include, but are definitely not limited to, the following:

PVP (poly N-vinyl-2-pyrrolidone) is an excellent film-former that is substantive to hair, forms clear films, and is completely water soluble. However, it absorbs water readily, which in humid weather makes it sticky or tacky to the touch, can cause frizz, and give a dull appearance to the hair. In dry weather, it can become brittle and flaky.

PVA (polyvinyl acetate) resists absorption of water in high humidity (which leads to better hold in damp weather conditions) and is more flexible in dry weather so it doesn't flake, but is not as substantive to hair.

PVP/VA copolymer provides an excellent compromise between the properties of each of these polymers individually.

Polyurethane (good thermal stability), acrylic copolymer, polyacrylates, acrylates copolymer, and other copolymers are also all hold agents found in hair gels.

Cationic polymers (Polyquaternium): These positively-charged polymers are very substantive to the negatively-charged surfaces of human hair. For this reason, some cationic polymers have been found to be useful in hair styling applications. They form clear, glossy films and decrease static-charge buildup and fly-away hair. They typically provide good wet and dry combing results and impart a smooth feel to the hair.

Polyquaternium-4 : is a superior film-former on the hair, and has been found to exhibit very high curl retention even in humidity. It is very substantive to hair, but exhibits little build-up. It is very stiff due to its molecular structure, and is thus outstanding for use in hair gels.

Polyquaternium-11: is copolymer of VP/DMAEMA (vinyl pyrrolidone and dimethylaminoethyl methacrylate). As a copolymer of VP and an acrylate, it is less susceptible to humidity than VP homopolymer. However, it may have more potential for failure due to humidity than polyquaternium-4. Polyquaternium-11 is generally recommended for mousses and creams, where it can moisturize as well as aid in styling. This polymer is water miscible, but not water soluble. This could lead to some build-up over time if one were not using a clarifying shampoo occasionally. There are many more polymers, copolymers, combinations of polymers, and new additives for hair gels that are being used in commercially available formulas, and even more being developed in laboratories. Many of these provide better rinsability, more softness, and a tougher film with better hold. We may explore some of these newer ideas and technologies in a future article.

To sum it up

If you live in a humid, hot environment, you should avoid a product containing PVP as an ingredient. If you are in a dry, cold climate, you should seek a product with Polyquaternium-11. Humectant additives--panthenol, propylene glycol, glycerin--may help product performance in a dry climate also, but may be disastrous in a humid one. As always, experimentation will be necessary to find the product that is right for you and your hair.

This article was originally published in January 2008, and has been updated for grammar and clarity.