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Hair and scalp physiology

Img_Hair and scalp physiology

With a surface area of approximately 600 cm2, the scalp is a protective, physical barrier from which the hair grows. Hair is highly resistant and made from keratin. An adult has between 100,000 and 150,000 strands of hair on his/her head.

The scalp: a physical barrier and thermal insulator

The scalp,made of the soft tissues that covers the skull, is a continuous, supple, resistant outer layer. It is divided into several layers, the one closest to the surface of which contains the hair bulbs that hold the hair.   In fact, the scalp has the same structure as skin.  It plays several roles: physical barrier, immunologic protection, thermal insulation...   The cellular renewal process in the scalp normally takes 2 weeks. However, if there is inflammation, this process may accelerate. The cell renewal process in skin cells takes longer as compared to the scalp: 3 weeks rather than 2.  The dead skin cells on the scalp shed in the form of tiny, invisibles scales. Nevertheless, in the case of inflammation and excessive scaling, dead cells accumulate in clusters and thus become visible. This is called dandruff.

Hair: extremely resistant

The main function of hair is to protect the head. Hair comprises one part that lies above the skin, the hair shaft and another part that lies underneath the skin, the root. The hair shaft grows out of the scalp’s surface whereas the root is embedded in the hair follicle. The hair follicle is the hair’s ‘production unit’. Each day, all of our hair follicles produce a million new keratinocytes. These cells synthesize keratin, a fibrous structural protein that is the primary component of hair, which makes it extremely resistant. At its inner base, the hair follicle has a bulb, called the dermal papilla, where several small blood vessels filled with nutrients and oxygen that are necessary for hair growth, come together. Above this bulb is the sebaceous gland, which produces sebum. Thus, the hair is permanently lubricated. The hair shaft comprises three different parts: the medulla, surround by the cortex, which is enveloped in the cuticle. Its color varies, depending on the individual. An adult has between 100,000 and 150,000 strands of hair on his/her head.


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