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lentigos, are flat, tan to dark brown or black patches of skin caused by long-term sun exposure. They usually develop by middle age in areas of skin (such as the hands, face, and chest) that have been repeatedly exposed to the sun.

Cherry angiomas

Cherry angiomas (see page 1059) are flat or dome-shaped small red spots on the skin that are caused by leaks in blood vessels. Although they can first appear in early adulthood, cherry angiomas usually result from a loss of elasticity in the skin that occurs as people age.

Dysplastic nevi

Dysplastic nevi are large, round moles that have not been present from birth. They usually appear around puberty but can occur at any age. Dysplastic nevi usually have irregular borders with indistinct margins and may be slightly asymmetrical. They can be varying shades of tan or brown and darker in the center. Dysplastic nevi should be examined regularly by a doctor because they can become cancerous (malignant melanoma; see page 1069).

Normal moles

Moles are round or oval spots on the skin that are pigmented with melanin, the substance that gives skin, hair, and eyes their color. Moles are very common. They can be flat (top left and right) or evenly raised (bottom left and right) and are usually clearly outlined against surrounding skin. Large moles may have coarse hairs growing out of them. Some people have many moles all over their body (dysplastic nevi; above right). Some moles can become cancerous (malignant melanoma; see page 1069).

Skin Cancer

Basal cell carcinoma

Basal cell carcinoma (see page 1068) is a common form of skin cancer usually caused by overexposure to the sun. Basal cell carcinomas grow slowly, rarely spread, and are seldom life-threatening. They vary in appearance but usually start as small, flat nodules that gradually turn into ulcers (open sores) with raised edges. A close-up of one type of basal cell carcinoma is shown here (left). Basal cell tumors frequently appear on the face, usually around the eyes, near the nose (center) or on the nose (right) and on other sun-exposed areas (including the back, chest, arms, and legs).

Squamous cell carcinoma

Squamous cell carcinoma (see page 1069) is a common skin cancer that is rarely life-threatening. Squamous cell tumors start as small, firm, usually painless lumps or patches and can resemble warts or ulcers (open sores). They are associated with sun exposure and can occur anywhere on the body but are common on the backs of the hands (as shown here) or on the lips. In rare cases, squamous cell tumors can spread to other parts of the body and can be fatal, especially if they develop in a scar from a burn or vaccination.

MALIGNANT MELANOMA

Malignant melanoma

Malignant melanoma (see page 1069) is the most deadly form of skin cancer. It is sometimes associated with exposure to the sun but can occur anywhere on the body, including parts of the body that are normally not exposed to the sun. Malignant melanomas most often appear on the face, upper trunk, or legs, and usually grow from existing moles, although they can also develop on seemingly normal skin. Malignant moles may bleed and can resemble sores that don’t heal.

Asymmetry

Cancerous moles are often asymmetrical—one half of the mole looks different from the other half if you draw an imaginary line horizontally or vertically through the center of it.

Border

The outline of a cancerous mole can be uneven or have poorly defined edges and may change over time. Normal moles have clean borders.

Color

Melanomas can be very dark and can contain shades of tan, brown, white, red, or blue. They can also change color.

Diameter

Moles or colored areas of skin that grow larger than ½ inch across (about the width of a pencil eraser) may be a sign of malignant melanoma, although smaller moles can also indicate malignant melanoma.

Dermatitis

Irritant dermatitis

Irritant dermatitis (see page 1062) is a nonallergic form of contact dermatitis caused by exposure to any substance (including soap and water)