The Physiology of the Skin and How Cosmetics Affect Skin Functio


Skin is made up of three main layers: the epidermis, the dermis and the hypodermis (see picture).Cross section image of human skinThe epidermis is the only layer we can see with our eyes and as we age, remarkable changes occur which are hidden from our view. For instance, the skin gradually thins over time, especially around the eyes. Some cosmeceuticals can minimally re-thicken the skin, but the process of thinning is inevitable. Elastin and collagen, located in the dermis keep the skin resilient and moist, but with aging these fibers break down to create lines and wrinkles. Exposure to ultraviolet radiation accelerates this process, and since few cosmetics can actually reach the dermis, the idea that a cosmetic can reverse this process is unfounded. The best way to prevent fine lines and wrinkles is to limit our exposure to the sun and ultraviolet radiation.

The skin is a highly complex, dynamic tissue system. One square inch of the skin is composed of 19 million cells, 625 sweat glands, 90 oil glands, 65 hair follicles, 19 000 sensory cells and 4 metres of blood vessels (Lappe, 1996). The outermost layer of the epidermis is called the cornified layer, and is made of sheets of keratin, a protein, and squames, dead, flat skin cells. It is our barrier against dehydration from the environment. It receives its primary supply of moisture from the underlying tissue, since constant contact from the external environment tends to dry out the skin’s surface. When the skin is exposed to dry conditions, the cornified layer can become dry, brittle, firm and if untreated, it can crack and lead to infection. Creams create a waxy barrier to prevent dehydration and keep the skin moist and supple. Underneath the cornified layer lie six more layers of the epidermis responsible for cell generation. The life cycle of skin cells within this layer takes approximately 28 days, so it may take three to four weeks to observe any changes at the skin’s surface from using a new cosmetic.

The skin surface is also home to millions of healthy micro-organisms which increase our immunity to pathogenic, or disease-causing bacteria. Thus, our desire to sterilize the skin also destroys beneficial bacteria, such as streptococcus mutans, and micrococcus luteus . Toners, for instance, are beneficial in keeping bacterial populations down, thus reducing acne flare-ups resulting from microbes which invade and proliferate in the pores. Over use of anti-microbial agents can produce harmful results when too many beneficial bacteria are destroyed, allowing pathogenic bacteria to multiply unchecked on the skin. The skin also produces antimicrobial proteins, two of which are called defensins and cathelicidins, which increase when the skin is damaged. Perspiration, necessary for the maintenance of internal body temperature, also excretes a germicidal protein called dermicidin to combat bacteria producing body odor. Deodorants also assist in keeping the bacterial population down, thus decreasing the odors produced as they feed on the waste matter excreted by the sweat glands. Research has shown that people who wash excessively are more prone to infection and eczema as a result of ‘washing” away natural bacteria and germicides too frequently.

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