AQUIS co-founder and ceo, Suveen Sahib, has been studying hair health for the past five years. Here we explain how skin and hair are alike, with nature having gifted both of these natural barriers to protect skin and hair from unwanted and damaging elements. 

What makes our skin a protective barrier? Data has shown for decades that our skin surface is composed of a “brick and mortar” layer, called the stratum corneum. This superficial layer is really tiny, usually around a couple dozen microns in thickness 1, but it plays a huge role: it acts as a protective barrier against water loss and hazard penetration 2,3 .

Just think of your skin as a wall. The stratum corneum is composed of “brick”, the corneocytes that are dead flat skin cells embedded in a “mortar”, a lipidic matrix that sticks the cells together 4,5. This unique organization helps to maintain its protective function, just like the walls of your house: it encloses your body from the external environment.

Meet the lipids, these natural “cement” components that play a key role to keep our skin healthy. The most dominant lipid from our cement are called ceramides 6. They have a key role in skin protection - it has been shown that ceramides can be lacking in damaged skin.

Why does it matter? When our skin is damaged either by a skin condition, such as eczema or psoriasis, or by external factors, like harsh ingredients such as alcohol or UV rays, our natural protective barrier is affected; for example, lipids from the stratum corneum can be swiped away and disorganized 7,8. The protective function from this barrier is in consequence, affected by a loss of organization and cohesiveness.

Same for our hair! Interestingly, even if the hair is a dead component, unlike the skin, it does contain a similar protective layer. Healthy human hair is coated by seven layers of cuticle cells. Cuticles are dead cells like corneocytes called cortical cells 9, 10.

Healthy hair - cuticles lay flat - water rolls off

The epicuticle, “the stratum corneum” of the hair. The outermost layer called the epicuticle, plays a crucial protective function for the hair, just like the stratum corneum for skin. The cuticles protect from external hazard and penetration 11.

And guess what comes next in our hair protection? A special hair lipid and biome system. Not only at the skin surface do lipids have a key protective role. If we look at the hair surface organization, data show that lipids also play a crucial role in the protective hair function 9.

As part of the skin, hair also supports its own microbial habitat. Cuticles that are healthy contain a dominant lipidic class: 18-methyleicosanoic acid (18-MEA).

Regarding the hair biome, its precious microbial habitat shows a unique microorganism community, that is even more diverse on long hair compared to shorter hair. The bacterial profile of hair length is different from the population in the follicle and it also varies by geographical origin ref scientific report.

The lipids strongly bond to the underlying proteins 11 and are key to our hair and scalp health. Their protective properties cannot be simply replaced by using products or surface coatings.

Protecting this surface ecosystem of lipids and microbiome is crucial for maintaining healthy hair 12. Our haircare routine and the products we use change scalp sebum excretion, barrier function and pH, all of which have a direct influence on our precious hair ecosystem and impact the biome. Ref biome scalp

When the 18-MEA layer is disrupted or missing, hair loses its capacity to resist water and becomes more vulnerable to simple things like daily haircare, such as shampooing.

Damaged hair - hair cuticles are raised allowing water and chemicals to penetrate

This protective layer can often be lost through chemical treatments such as bleaching or even sunlight. It was recently revealed that aging also causes loss of 18-MEA, especially over the age of 40. When this lipidic layer is lost, hair becomes drier and there is a risk of diffusion of external elements into the hair which includes water. Water doesn’t stay at the hair surface but tends to penetrate the hair 10,13   and weaken it considerably. The effect of water is more pronounced for colored and chemically treated hair, which is already weakened to begin with by these treatments. Presence of hard water also has a compounding effect when it comes to colored and treated hair.

Just like we have our daily skincare routine to take the best care of our skin,
it is important to carefully choose what we put in our hair and to implement a haircare routine using gentle products that work with the biology of the hair, as well as prevent damage to the protective hair barrier and biome system, maintaining hair at its optimum health over the years.

Learn more about how AQUIS protects your hair


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  • Spatial and Environmental Variation of the Human Hair Microbiota: Lauren Brinkac,Thomas H Clarke, Harinder Singh, Chris Greco, Andres Gomez