General Considerations

The skin, which is the largest organ of the body, is one of the best indicators of general health. Even a person without medical training is capable of detecting changes in skin color and texture. The trained examiner can detect these changes and at the same time evaluate more subtle cutaneous signs of systemic disease.

Diseases of the skin are common. Approximately one third of the population in the United States has a disorder of the skin that warrants medical attention. Nearly 8% of all adult outpatient visits are related to dermatologic problems. Nonmelanoma skin cancers, basal cell carcinomas, and squamous cell carcinomas are by far the most common malignancies that occur in the United States. One of every three new cancers is a skin cancer, and the vast majority are basal cell carcinomas. About 80% of the new skin cancer cases are basal cell carcinoma, 16% are squamous cell carcinoma, and 4% are melanoma. The American Cancer Society estimates that there are more than 65,000 new cases of basal cell carcinoma annually. Most of these cases occur on the head and neck, which is evidence of the importance of sun exposure as a causative stimulus. Squamous cell carcinoma, the second most common skin cancer after basal cell carcinoma, afflicts more than 200,000 Americans each year. Although in most of these patients the cancer is treated and cured, skin cancer still causes more than 5000 deaths a year.

The incidence of malignant melanoma is rising at a rate faster than that of any other tumor;it has more than tripled among white persons between 1980 and 2004. It was estimated that there were approximately 59,940 new cases of melanoma in 2007: 33,910 in men and 26,030 in women. There were 8110 total deaths estimated in 2007 from melanoma. In 2007, the lifetime risk of developing melanoma (invasive and in situ) for all races was 2.76%;in white persons, the lifetime risk was 3.15%, and in African Americans, it was 0.11%. In 2006, invasive melanoma was the fifth most common cancer diagnosed in men and the sixth most common cancer in women. Six of every seven deaths from skin cancer in the United States are caused by melanoma. The incidence of melanoma has increased 7% per year since the early 1990s. The reasons for this are unclear, but excessive sun exposure is a major factor.

Early detection and treatment of malignant melanoma, as with most cancers, offers the best chance of a cure. Both basal cell carcinoma and squamous cell carcinoma have a better than 95% cure rate if detected and treated early. Among patients with a superficial melanoma (<0.76 mm in depth), the survival rate is more than 99%, whereas among those with a larger lesion (>3.64 mm in depth), the 5-year survival rate is only 42%. The external nature of melanoma gives the examiner an opportunity to detect these small, curable lesions.

The most important function of the skin is to protect the body from the environment. The skin has evolved in humans to be a relatively impermeable surface layer that prevents the loss of water, protects against external hazards, and insulates against thermal changes. It is also actively involved in the production of vitamin D. The skin appears to have the lowest water permeability of any naturally produced membrane. Its barrier to invasion retards potentially noxious agents from entering the body and causing internal damage. This barrier protects against many physical stresses and prohibits the invasion of microorganisms. By observing patients with extensive skin problems, such as burns, clinicians can appreciate the importance of this organ.

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