Part 2 book “ABC of dermatology” has contents: The sun and the skin, the sun and the skin, the skin and systemic disease—genetics and skin disease, cutaneous immunology—autoimmune disease and the skin, bacterial infection, viral infections, fungal and yeast infections, . and other contents. | 14 The sun and the skin R StC Barnetson People with darkly pigmented skin very rarely get skin cancer. Those of a Celtic constitution, when exposed to strong sunlight in countries such as Australia, get skin cancer very readily. Australia has the highest incidence of skin cancer in the world, with 140 000 new cases per year, and 1200 deaths per year, mainly from melanoma. It is therefore important to understand that there is a variation in skin sensitivity to sunlight. This is rated from one to six (Fitzpatrick classification). Skin type one subjects have red hair and do not tan, burn very easily in the sun and develop skin cancer readily, whereas skin type six subjects have black skin (with an inbuilt sun protection factor of 10) and very rarely develop skin cancer. This is a useful guide in assessing the risk of sun damage and in determining the dose of ultraviolet B in treatment. Skin types and sun • • • • • • Type 1—Never tans, freckles, red hair, blue eyes Type 2—Tans with difficulty, less freckled Type 3—Tans easily, dark hair, brown eyes Type 4—Always tans, Mediterranean skin Type 5—Brown skin (for example, Indian) Type 6—Black skin (for example, African) Ultraviolet radiation There are three types of ultraviolet radiation—the short wavelength ultraviolet C (100–280 nm), ultraviolet B (290– 320 nm), and long wavelength ultraviolet A (320–400 nm). Beyond this is visible light then infrared, and radiowaves. ultraviolet C does not penetrate beyond the stratosphere as it is absorbed by the ozone layer. Ultraviolet B is very important in both sunburn and the development of skin cancer. Ultraviolet A is thought to be of increasing importance in the development of skin cancer, and causes tanning but not sunburn. It is also important in people with photosensitivity. The effects of ultraviolet radiation may be classified as short term (sunburn, photosensitivity) or long term (skin cancer, wrinkling, solar elastosis, solar keratoses, seborrhoeic warts). There is
