The skin of an adult has an area of about 1.5 m2, a thickness of 1to 4mm. it is a resistant organ formed of about 2000 billion of cells which die periodically to be replaced by new healthy cells. The skin consists of three layers: epidermis, dermis and hypodermis.
The epidermis is the superficial layer of the skin that is in contact with the outside. It consists of three groups of cells: keratinocytes, melanocytes and Langerhans cells.
- The Keratinocytes migrate to the surface of the skin and renew regularly. They are filled with highly resistant filaments (keratin) and lipids that provide resistance to external aggression. During their migration, these cells gradually flatten and eventually die on the surface of the skin to be replaced by new cells. Melanocytes, as a result of radiation, produce melanin, the pigment that provides color of many tissues including the skin. Langerhans cells, playing a role in the immune system, protect the skin from pathogens: chemicals, viruses, bacteria, allergic factors, etc. Langerhans cells also identify abnormal cells and trigger their elimination.
The dermis is located just below the epidermis. Being rich in collagen fibers, it provides the skin its strength and elasticity. It is in the dermis that skin cells born and multiply to replace dead cells. Unlike the epidermis, the dermis contains many blood vessels that provide nutrition to its cells and those of the epidermis. In addition, there are in the dermis nerves that are sensitive to touch, pain and temperature; that sensitivity allows protection and repair of damaged tissues.
The hypodermis is the deepest layer of the skin. It is rich in fat and blood vessels which allow it to absorb the pressures to which the skin is subjected. In addition, the hypodermis protects the body from temperature variations. The hypodermis is found mainly in parts of the body that withstand significant impact: buttocks, heels, etc.
The skin is constantly faced with aggression and pathogenic attacks. Thanks to its immunity and protective actions, the skin can repair itself as long these attacks are not too damaging. Squamous cell carcinoma occurs when the skin is unable to defend itself against carcinogenic attacks.
Usually, squamous cell carcinoma develops on precancerous lesions of the skin (actinic keratosis). Repeated or untreated papillomavirus (HPV) infection can also cause the development of squamous cell carcinoma. In addition, intense and prolonged exposure to sunlight can lead to development of squamous cell carcinoma in people of fair skin.