RELATED STORIES • Freckles and moles: What's the difference? WOMEN'S HEALTH Hair/Nails/Skin • Corns and calluses • Diaper rash • Nail fungus • Shingles • Ingrown toenails • Moles • Acne • Psoriasis • Hair loss • Sweating and body odor • Rosacea • Hives and angioedema • Athlete's foot • Dermatitis/Eczema • Cold sore • Common warts • Cellulitis • Anal itching • Dandruff • Impetigo • Boils and carbuncles • Ringworm of the body • Jock itch • Plantar warts • Folliculitis • Dry skin • Actinic keratosis • Bedsores (Pressure sores) • Vitiligo • Lipoma • Tinea versicolor • Acanthosis nigricans • Molluscum contagiosum • Neurodermatitis (lichen simplex chronicus) • Morphea • Pityriasis rosea • Lichen nitidus • Bullous pemphigoid • Pyoderma gangrenosum • Lichen sclerosus • Ichthyosis vulgaris • Pilonidal cyst • Pemphigus • Sweet's syndrome • Sacral dimple • Dermatographia • Keratosis pilaris • Poison ivy rash • Lichen planus • Granuloma annulare • Dyshidrosis • Hidradenitis suppurativa • Henoch-Schonlein purpura • Hemangioma

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Moles, known medically as nevi, are clusters of pigmented cells that often appear as small, dark brown spots on your torso, face, arms and legs. But moles can come in a range of colors and can develop virtually anywhere, including your scalp, armpits, under your nails, and between your fingers and toes.

Most people have between 10 and 40 moles, although the number you have may change throughout life. New moles can appear into mid-adulthood, and because moles last about 50 years, some moles may disappear as you age.

The great majority of moles are harmless, but in rare cases, moles may become cancerous. Monitoring moles and other pigmented patches is an important step in the diagnosis of skin cancer, especially malignant melanoma. Although not all melanomas develop from pre-existing moles, many begin in or near a mole or other dark spot on the skin.

Although the typical mole is a plain, brown spot, moles come in a wide variety of colors, shapes and sizes. They can be flesh-colored, reddish-brown, medium to dark brown, or blue; vary in shape from oval to round, and be as small as a pinhead or large enough to cover an entire limb. Moles that are larger than 8 inches in diameter and present at birth are a special problem. They may need to be removed to avoid the risk of malignant melanoma, the most deadly form of skin cancer.

The surface of a mole can be smooth or wrinkled, flat or raised. Sometimes a mole may start out flat and brown and later become slightly raised and lighter in color. Some may become raised enough that they form a small stalk and are eventually rubbed off. Others may simply disappear.

Although most moles develop by age 20, they can continue to appear until midlife. There are also certain times in your life when moles are more apt to change; for example, they're likely to become darker, larger and more numerous because of hormonal changes during adolescence and pregnancy and with the use of birth control pills.

Melanin is a natural pigment that gives your skin its color. It's produced in cells called melanocytes, either in the top layer of the skin (epidermis) or the outer layers of the skin's second layer (dermis). Melanin is then transported to the surface cells of your skin. Normally, melanin is distributed evenly, but sometimes melanocytes grow together in a cluster, giving rise to moles.

Scientists don't know why moles develop or what purpose they serve, if any, although they do appear to be determined before birth. Most moles are harmless and don't require special care, but some people have unusual-looking moles, called dysplastic nevi, which are more likely to turn cancerous than ordinary moles are. Atypical moles occur most often on the back in both men and women, and also on the abdomen, chest and legs in women.

Several types of moles have a higher than average risk of becoming cancerous. They include:

• Large moles present at birth. Large moles that are present at birth are called congenital nevi or giant hairy nevi. These moles may increase your risk of malignant melanoma, a deadly form of skin cancer. In general, moles that are more than the size of an adult open palm pose the greatest risk. Have your doctor examine any mole that was present at birth and is palm-sized or larger.
• Moles that run in families. Moles that are larger than average — which is about 1/4 inch (6 millimeters), or the diameter of a pencil eraser — and irregular in shape are known as atypical (dysplastic) nevi. These moles tend to be hereditary. They're frequently described as looking like fried eggs because they usually have dark brown centers and lighter, uneven borders. Overall, they may look red or tan. If you have dysplastic nevi, you have a greater risk of developing malignant melanoma.
• Numerous moles. If you have many moles larger than a pencil eraser, you are at greater risk of developing melanoma.

If a new mole appears past age 20, see your doctor. These signs and symptoms may indicate a medical concern:

• Painful
• Itching or burning
• Oozing or bleeding
• Inflamed
• Scaly or crusty
• Suddenly different in size, shape, color or elevation

If you're concerned about any mole, see your doctor or ask for a referral to a dermatologist.

You may choose to make a skin examination a regular part of your preventive medical care. Talk to your doctor about a schedule that's appropriate for you. A general guideline is every three years for people ages 20 to 39, and annually for people age 40 or older.

Your doctor will examine your skin from head to toe, including your scalp, your palms, the soles of your feet and the skin between your buttocks. If your doctor suspects that a mole may be cancerous, he or she may take a sample of the tissue (biopsy) and submit the biopsy for microscopic examination.

If your doctor takes a tissue sample of the mole and finds it to be cancerous, the entire mole and a margin of normal tissue around it needs to be removed. Usually a mole that has been removed won't reappear. If it does, see your doctor promptly.

Treatment of most moles usually isn't necessary. For cosmetic reasons, a mole can be removed in several ways:

• Shave excision. In this method, your doctor numbs the area around a mole and then uses a small blade to shave off the mole close to your skin.
• Punch biopsy. Your doctor may remove a mole with a small incision or punch biopsy technique, which uses a small cookie-cutter-like device.
• Excisional surgery. In this method, your doctor cuts out the mole and a surrounding margin of healthy skin.

These procedures are usually performed in the office of your doctor or dermatologist and take only a short time.

The best way to catch potential problems at an early stage is to become familiar with the location and pattern of your moles. Examine your skin carefully on a regular basis — monthly if you have a family history of melanoma, and at least every three months otherwise — to detect early skin changes that may signal melanoma.

Remember to check areas that aren't exposed to sunlight, including your scalp, armpits, feet (the soles and between the toes), genital area and, if you're a woman, the skin underneath your breasts. If necessary, use a hand-held mirror along with a wall mirror to scan hard-to-see places such as your back. People with dysplastic nevi are at greater risk of developing malignant melanoma and may want to consider having a dermatologist check their moles on a regular basis.

To detect melanomas or other skin cancers, use the A-B-C-D skin self-examination guide, adapted from the American Academy of Dermatology:

• A is for asymmetrical shape. Look for moles with irregular shapes, such as two very different-looking halves.
• B is for irregular border. Look for moles with irregular, notched or scalloped borders — the characteristics of melanomas.
• C is for changes in color. Look for growths that have many colors or an uneven distribution of color.
• D is for diameter. Look for growths that are larger than about 1/4 inch (6 millimeters).

In addition to periodically checking your moles, you can take protective measures to protect yourself from cancerous changes:

• Avoid peak sun times. It's best to avoid overexposure to the sun, but if you must be out of doors, try to stay out of the sun from 10 a.m. to 4 p.m., when ultraviolet rays are most intense.
• Use sunscreen. Twenty to 30 minutes before going outdoors, apply sunscreen with a sun protection factor (SPF) of at least 15. Reapply every two hours, especially if you're swimming or involved in vigorous activities. Some sunscreens contain substances that block both types of ultraviolet rays, ultraviolet A (UVA) and ultraviolet B (UVB). Choose sunscreens with avobenzone, titanium dioxide, or transparent or microdispersed zinc oxide listed on the ingredient label. And keep in mind that sunscreen is just one part of a total sun protection program.
• Cover up. Broad-brimmed hats, long sleeves and other protective clothing also can help you avoid damaging UV rays. You might also want to consider clothing that's made with fabric specially treated to block UV radiation.

If you have a mole that's unattractive, you may choose to cover it up using makeup designed to conceal blemishes and moles. If you have a hair growing from a mole, it may be possible to clip it close to the skin's surface. Dermatologists also can permanently remove hair from moles. If you have a mole in a beard, you may want to have it removed by your doctor because shaving over it repeatedly may cause irritation. You may also want to have moles removed from other parts of your body that are vulnerable to trauma and friction.

Anytime you cut or irritate a mole, be sure to keep the area clean. See your doctor if the mole doesn't heal.