What are the differences and similarities between scalp and skin?

Scalp: what are the differences and similarities with the skin?

Scalp and skin: some similarities

The scalp is nothing else than an extension of the skin. It has three layers like the other areas of the face and body.

The epidermis is a very thin layer made up of four layers: stratum basal, stratum spinosum, stratum granulosum and, finally, the outermost layer stratum corneum. These specific layers are formed by the differentiation of keratinocytes from the basal layer into corneocytes in the stratum corneum. The epidermis is protected by a lipid layer thanks to this keratinocyte differentiation phase. Between the dermis and the epidermis lies the dermal-epidermal junction, an important link in the skin's integrity, containing many types of collagen and anchoring filaments.

The dermis is a highly vascularized area of the scalp. It is thick, averaging 2.5 millimeters. This is where the hair root is located: the hair follicle, invaginated in the dermis. Surrounded by a rich vascular network, it benefits from a significant supply of energy, essential for hair growth and promoting cell survival and renewal. It also contains the sebaceous glands, responsible for the synthesis and secretion of sebum. The dermis acts as a water reserve (80% of the skin's reserves). It is rich in hygroscopic molecules that give the skin its tone and suppleness. Thanks to a dense network of collagen and elastin fibers, it also acts as a support tissue and mechanical protection.

L'hypoderme est la composante la plus profonde du cuir chevelu, une réserve d'énergie graisseuse. Il protège le corps des chocs, agit comme un manteau thermique et se trouve à l'interface entre le derme et les structures mobiles sous-jacentes telles que les muscles et les tendons.

Differences between scalp and skin

Nevertheless, the scalp has a few special features. It is the thickest skin on the body (up to 8mm). Compared to the rest of our skin, the scalp has more blood vessels and hair follicles (∼250/cm² vs 10-50/cm² on the rest of the body).

Each hair follicle has a sebaceous gland responsible for producing sebum. These lipids naturally protect the scalp from environmental aggressions, lubricate hair fibers and help prevent water loss. The scalp is a very innervated area, which makes it highly sensitive to touch. The hair follicle is also highly vascularized, providing the bulb with oxygen and nutrients.

Finally, the scalp has a specific microbiota, mainly dominated by Malassezia species and C.acnes bacteria. Together with the scalp skin, this specific microbiota acts as the first line of defense against exogenous factors.

Scalp functions

Hair growth area

As we have already seen, the scalp differs from the skin of the body in the abundance of hair follicles it contains, the size of the hairs, and the number and volume of the sebaceous and sweat glands. It's a veritable reservoir of hair follicles, housed in huge numbers in the superficial layer, and innervated by a multitude of tiny blood vessels. This microcirculation supplies the hair bulbs with the nutrients and oxygen essential for hair growth. In this way, the bulb cells, the keratinocytes, can continuously produce the components of the hair fiber for strong, healthy hair.

A real protective barrier

The scalp acts as a protective barrier. Firstly, it acts effectively as a physical barrier, protecting the internal environment from the external environment and dehydration. The hydrolipidic film on the scalp's surface acts as a shield against aggression and regulates moisture levels. 

Involved in the thermal regulation mechanism, it is an excellent insulator, protecting the scalp from thermal aggression and maintaining a constant surface temperature. Perspiration contributes to this thermal insulation

It also provides immunological protection thanks to its naturally acidic pH, which protects against aggression, radiation and micro-organisms. Sebum also has a bactericidal function.

Scalp disorders

The scalp can suffer from problems such as irritation, oil imbalance or pellicle problems. These common skin problems are due to stress factors that can be linked to an individual's genetics, lifestyle (diet, smoking, sleep, stress) or environment (pollution).

Because of its specific microbiota, the scalp can also present more specific disorders. An imbalance in the microbiota can lead to an inflammatory disorder. This is the case, for example, with seborrheic dermatitis caused by the yeast Malassezia furfur, resulting in dandruff and an oily scalp. Too much Corynebacterium striatum can lead to unpleasant odors.

So it's important to rebalance the scalp to avoid all these disorders. Having a healthy scalp will lead to beautiful hair.

Hair care skinification is a trend that involves treating the scalp like the skin: moisturizing, soothing, purifying... And as we've seen, this makes sense, since the scalp is an extension of the skin, albeit with a few specific characteristics that need to be taken into account (dandruff, balance, etc.).