18-mea layer

Advances in scientific characterization techniques have enabled us to obtain unprecedented levels of information about nanoscale materials due to the ability to both directly and indirectly observe these materials in situ (in their natural environment). Fortunately for us in the curly world, one complex biological system that has received study is human hair. Through use of new methods, scientists have been able to identify and study the role of the multitudes of subspecies and structures present in hair. This has provided us with new insight regarding the cuticle-cuticle cell membrane complex (CCMC), and its major lipid component, 18-methyl eicosanoic acid (18-MEA). We have found that this relatively small fatty acid plays a very important role in the health and beauty of our hair, and it is becoming a bit of a buzzword in the industry. What exactly is 18-MEA, and how does it make such an important contribution? Perhaps more importantly, how can we protect the 18-MEA levels in our hair or replenish it if we have depleted it?

Cuticle glue and cushion

The protective cuticle layer that encapsulates the outer portion of each hair strand is a highly complex biocomposite structure made up of multiple layers of overlapping protein scales. Between each layer of scales, there exists a region called the cuticle-cuticle cell membrane complex, which is comprised of several layers of both delta and beta protein structures, a significant amount of 18-MEA covalently bonded to the b-protein structure, and a small amount of unbound lipids such as oleic and palmitic acid. This entire structure acts as a protective cushion and cement between the cuticle scale layers.

The covalently-bonded 18-MEA is responsible for providing hair with its hydrophobicity (water-repellent property), which protects hair by preventing it from absorbing too much water from the environment. It also provides hair with softness, lubricity, and shine. More significantly, an intact layer of 18-MEA acts to decrease tangling in wet hair and in the transition from wet to dry, by encouraging adjacent hair strands to lie neatly in parallel to one another, smoothly aligned. It does this due to its ability to decrease surface friction by changing the receding contact angle of water. When hair is lacking 18-MEA, the strands become entangled and stuck to one another, and the hair dries more quickly in these tangled packets, resulting in greater tangling when hair is dry.

18-mea layer

Damage to the 18-MEA layer

18-MEA is not soluble in water and does not dissolve in most organic solvents, and since it is covalently bound, it is not easily removed via mechanical means. However, it is highly susceptible to alkaline hydrolysis and subsequent loss through rinsing, meaning that products and processes that use a higher pH possess the risk of destruction of your hair’s protective lipid layer. Loss of the protective 18-MEA layer renders hair hydrophilic, so that it absorbs too much water from the environment, which leads to frizz and physical damage to the hair due to swelling and breaking of structures. Hair lacking its lipid layer is also more prone to tangling, frizz, breakage, and loss of curl structure.

Some shampoos that have a higher pH, most soaps, and baking soda rinses can gradually deplete the 18-MEA layer in a cumulative fashion with each additional use. However, highly alkaline processes such as perm, relaxers, and synthetic dyes can cause sudden catastrophic depletion of the 18-MEA layer. For this reason, chemically processed hair is especially vulnerable to damage due to moisture and tangling. Loss of this 18-MEA layer is probably the characteristic we are describing when we say processed hair is porous. It is also important to note that exposure to light, both visible and ultraviolet (UV), also gradually decrease the 18-MEA content in hair.

Minimizing exposure to alkaline environments is one way to protect the health of your hair. Cleansers that have pH≤ 6.0 are the safest for your hair. Reducing the frequency with which you color or process your hair will also help. Protecting your hair from light is another good way to reduce loss of 18-MEA and other types of damage to your hair.

Replenishing the 18-MEA layer?

It would seem logical that we could just replace the 18-MEA that is removed from the hair by redepositing it via a product. However, we cannot exactly duplicate the work of nature, because 18-MEA is covalently bound to the beta-protein structure of the CCM. Fortunately, several companies have found that modified versions of 18-MEA (quaternized or delivered in mixtures with cationic surfactants) will selectively deposit onto the surface of damaged hair and can restore its hydrophobicity, decrease tangling and combing friction, and increase shine. The effect was found to be cumulative with additional uses of the product. Undamaged hair is unchanged when treated with these mixtures, so this is specifically beneficial to those with color or perm-damaged hair.

If your hair is damaged due to the use of alkaline processes or higher pH cleansing methods, replacing some of the lost 18-MEA will go a long way toward making your hair feel and look healthier and shinier. However, this is relatively new technology, so it is still challenging to find products exploiting these materials. Trevor Sorbie has an entire line based upon the beneficial properties of 18-MEA, called the “18-MEA Lipid Shine™ Line.”Another product line that contains 18-MEA is Scientific Essentials “Simply Scientific Hair™ Products.”