Skin diseases cause by unprotected sun exposure:

The UVB rays that lead to sunburn, also directly damage the cellular DNA which causes skin diseases such as actinic keratosis and skin cancer. Actinic keratosis is a pre-cancerous skin condition caused by too much exposure to the sun. AKs are usually small (less than 1/4 inch across), rough or scaly spots that may be pink-red or flesh-colored. Usually they start on the face, ears, backs of the hands, and arms of middle-aged or older people with fair skin, although they can occur on other sun-exposed areas. People who have them usually develop more than one. AKs tend to grow slowly and usually do not cause any symptoms (although some might be itchy or sore). A small percentage of AKs may turn into squamous carcinomas.

How skin cancer develops:

Most skin cancers start in the top layer of skin, called the epidermis. There are 3 main types of cells in this layer:

 

Basal cells: 

These cells are in the lower part of the epidermis called the basal cell layer or (stratum germinativum). These cells constantly divide to form new cells to replace the stratum corneum or squamous cells that are shed from the skin’s surface. Skin cancers that start in the basal cell layer are called basal cell carcinomas. Basal cell carcinoma is the most common type of skin cancer and represents 70-80% of skin cancers. These cancers develop on sun-exposed areas, especially the face, head, and neck. They tend to grow slowly and it’s rare for a basal cell cancer to spread to other parts of the body. However, if left untreated, basal cell cancer can grow into nearby areas and invade the bone or other tissues beneath the skin. If not removed completely, basal cell carcinoma can reoccur in the same place on the skin. People who have had basal cell skin cancers are also more likely to get new ones in other places.

Squamous cells:

These are flat cells in the upper part of the epidermis, which are constantly shed as new ones form. When these cells grow out of control, they can develop into squamous cell carcinoma. About 2 out of 10 skin cancers are squamous cell carcinomas. These cancers commonly appear on sun-exposed areas of the body such as the face, ears, neck, lips, and backs of the hands. They can also develop in scars or chronic skin sores elsewhere and sometimes start as actinic keratosis. Squamous cell carcinomas can usually be removed completely, although they are more likely than basal cell cancers to grow into deeper layers of skin and spread to other parts of the body.

Melanocytes:

These cells produce the brown pigment called melanin, which gives the skin its tan or brown color. Melanin acts as the body’s natural sunscreen, protecting the deeper layers of the skin from some of the harmful effects of the sun. Melanoma skin cancer starts in these cells. Melanoma is less common than some other types of skin cancer, but it is more likely to grow and spread to other parts of the body. Exposure to ultraviolet (UV) rays is a major risk factor for most melanomas with sunlight as the main source of UV rays. The risk of melanoma is much higher for Caucasians than for African Americans. Caucasians with red or blond hair, blue or green eyes, or fair skin that freckles or burns easily are at increased risk. Your risk of melanoma is higher if one or more of your first-degree relatives (parents, brothers, sisters, or children) has had melanoma. Approximately 10% of all people with melanoma have a family history of the disease.