Squamous cell carcinomas (SCC) are the second most common skin cancer in humans. The incidence of SCCs in the USA in 2012 was estimated at 700,000 casesSCCs have a metastatic course in 3% to 5% of cases that is of poor prognosis. In men, the SCCs of the scalp represent the most frequent location of the head and neck, the 3rd location of the whole body. The SCCs of the scalp are more undifferentiated than in other locations. In addition, actinic keratoses of scalp, precursors of SCC, are more resistant to treatment than in other areas. These particularities of the SCCs of the scalp suggest the existence of specific factors at the epidermis level of the scalp.

UV-induced damage to DNA is the defining event in skin photocarcinogenesis. It has already been shown that DNA damage induced by UV and the kinetics of repair of this damage may vary with age or phototype of patients, but the topographic variation of DNA damage has never been studied, although it is known that gene expression in skin cells may differ from one region of the body to another.

the hypothesis is therefore that the particular characteristics of KAs and SCCs at the scal level could be explained by an increased sensitivity to UV-induced damage. It is planned to study UV-induced damage and its repair at the scalp level in humans compared to the forearm.

Inclusion Criteria:

• Male subject
• Subject aged 40 to 60 years
• Subject of phototype III or IV
• Subject with no skin lesions on the scalp and forearms
• Subject who has not been exposed to the sun for at least 1 month
• Subject affiliated to social security
• Subject who signed the informed consent form

Exclusion Criteria:

• Subjects with photosensitivity,
• Subject taking photosensitizing drugs
• Subjects with a history of skin cancer
• Subjects with abnormal healing
• Subjects with immunosuppression