Moles are growths on the skin. Doctors call moles nevi (one mole is a nevus). These growths occur when cells in the skin, called melanocytes, grow in a cluster with tissue surrounding them. Moles are usually pink, tan, brown, or flesh-colored. Melanocytes are also spread evenly throughout the skin and produce the pigment that gives skin its natural color. When skin is exposed to the sun, melanocytes produce more pigment, causing the skin to tan, or darken.

Moles are very common. Most people have between 10 and 40 moles. A person may develop new moles from time to time, usually until about age 40. Moles can be flat or raised. They are usually round or oval and no larger than a pencil eraser. Many moles begin as a small, flat spot and slowly become larger in diameter and raised. Over many years, they may flatten again, become flesh-colored, and go away.

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Dysplastic Nevi

About one out of every ten people has at least one unusual (or atypical) mole that looks different from an ordinary mole. The medical term for these unusual moles is dysplastic nevi. The “Pictures of Ordinary Moles and Dysplastic Nevi” section shows the differences between ordinary moles and dysplastic nevi.

Doctors believe that dysplastic nevi are more likely than ordinary moles to develop into a type of skin cancer called melanoma. Because of this, moles should be checked regularly by a doctor or nurse specialist, especially if they look unusual; grow larger; or change in color, outline, or in any other way.

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Melanoma is a type of skin cancer — one of the most serious types because advanced melanomas have the ability to spread to other parts of the body. (Melanoma can also develop in the eye, called intraocular melanoma, or rarely in other parts of the body where pigment cells are found. The CIS can provide information about the diagnosis and treatment of intraocular melanoma.) Melanoma begins when melanocytes (pigment cells) gradually become more abnormal and divide without control or order. These cells can invade and destroy the normal cells around them. The abnormal cells form a growth of malignant tissue (a cancerous tumor) on the surface of the skin. Melanoma can begin either in an existing mole or as a new growth on the skin. The “Pictures of Melanoma” section shows examples of melanoma. A doctor or nurse specialist can tell whether an abnormal-looking mole should be closely watched or should be removed and checked for melanoma cells. The purpose of routine skin exams is to identify and follow abnormal moles.

The removal of the entire mole or a sample of tissue for examination under a microscope is called a biopsy. If possible, it is best to remove moles by an excisional biopsy, rather than a shave biopsy.

If the biopsy results in a diagnosis of melanoma, the patient and the doctor should work together to make treatment decisions. In many cases, melanoma can be cured by minimal surgery if the tumor is discovered when it is thin (before it has grown downward from the skin surface) and before the cancer cells have begun to spread to other places in the body. However, if melanoma is not found early, the cancer cells can spread through the bloodstream and lymphatic system to form tumors in other parts of the body. Melanoma is much harder to control when it has spread. The spread of cancer is called metastasis.

Doctors and scientists believe that it is possible to prevent many melanomas and to detect most others early, when the disease is more likely to be cured with minimal surgery. In the past several decades, an increasing percentage of melanomas have been diagnosed at very early stages, when they are quite thin and unlikely to have spread. Learning about prevention and early detection, while important for everyone, is especially important for people who have an increased risk for melanoma. People who are at an increased risk include those who have dysplastic nevi or a very large number of ordinary moles.

Risk Factors for Melanoma

  • Family history of melanoma
  • Dysplastic nevi
  • History of melanoma
  • Weakened immune system
  • Many ordinary moles (more than 50)
  • Ultraviolet (UV) radiation
  • Severe, blistering sunburns
  • Freckles
  • Fair skin

The National Cancer Institute booklet What You Need To Know About™ Melanoma has more information about risk factors for this disease.

It is important to remember that not everyone who has dysplastic nevi or other risk factors for melanoma gets the disease. In fact, most do not. Also, about half the people who develop melanoma do not have dysplastic nevi, and they may not have any other known risk factor for the disease. At this time, no one can explain why one person gets melanoma while another does not. Research has shown that sun exposure, especially excessive exposure that leads to bad, blistering sunburns, is an important and avoidable risk factor. Scientists are continuing their studies of risk factors for melanoma.

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Prevention of Melanoma

The number of people in the world who develop melanoma is increasing each year. In the United States, the number has more than doubled in the past 20 years. Experts believe that much of the worldwide increase in melanoma is related to an increase in the amount of time people spend in the sun.

Ultraviolet (UV) radiation from the sun and from sunlamps and tanning booths damages the skin and can lead to melanoma and other types of skin cancer. (Two types of ultraviolet radiation — UVA and UVB — are explained in the “Dictionary” section.) Everyone, especially those who have dysplastic nevi or other risk factors, should try to reduce the risk of developing melanoma by protecting the skin from UV radiation. The intensity of UV radiation from the sun is greatest in the summer, particularly during midday hours. A simple rule is to avoid the sun or protect your skin whenever your shadow is shorter than you are.

People who work or play in the sun should wear protective clothing, such as a hat and long sleeves. Also, lotion, cream, or gel that contains sunscreen can help protect the skin. Many doctors believe sunscreens may help prevent melanoma, especially those that reflect, absorb, and/or scatter both types of ultraviolet radiation. Sunscreens are rated in strength according to a sun protection factor (SPF). The higher the SPF, the more sunburn protection is provided. Sunscreens with an SPF value of 2 to 11 provide minimal protection against sunburns. Sunscreens with an SPF of 12 to 29 provide moderate protection. Those with an SPF of 30 or higher provide high protection against sunburn. Sunglasses that have UV-absorbing lenses should also be worn. The label should specify that the lenses block at least 99 percent of UVA and UVB radiation.

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Early Detection of Melanoma

Because melanoma usually begins on the surface of the skin, it often can be detected at an early stage with a total skin examination by a trained health care worker. Checking the skin regularly for any signs of the disease increases the chance of finding melanoma early. A monthly skin self-exam is very important for people who have any of the known risk factors, but doing skin self-exams routinely is a good idea for everyone.

Here is how to do a skin self-exam:

  • After a bath or shower, stand in front of a full-length mirror in a well-lighted room. Use a hand-held mirror to look at hard-to-see areas.
  • Begin with the face and scalp and work downward, checking the head, neck, shoulders, back, chest, and so on. Be sure to check the front, back, and sides of the arms and legs. Also, check the groin, the palms, the fingernails, the soles of the feet, the toenails, and the area between the toes.
  • Be sure to check the hard-to-see areas of the body, such as the scalp and neck. A friend or relative may be able to help inspect these areas. Use a comb or a blow dryer to help move hair so you can see the scalp and neck better.
  • Be aware of where your moles are and how they look. By checking your skin regularly, you will become familiar with what your moles look like. Look for any signs of change, particularly a new black mole or a change in outline, shape, size, color (especially a new black area), or feel of an existing mole. Also, note any new, unusual, or “ugly-looking” moles. If your doctor has taken photos of your skin, compare these pictures with the way your skin looks on self-examination.
  • Check moles carefully during times of hormone changes, such as adolescence, pregnancy, and menopause. As hormone levels change, moles may change.
  • It may be helpful to record the dates of your skin exams and to write notes about the way your skin looks. If you find anything unusual, see your doctor right away. Remember, the earlier a melanoma is found, the better the chance for a cure.

In addition to doing routine skin self-exams, people should have their skin checked regularly by a doctor or nurse specialist. A doctor can do a skin exam during visits for regular checkups. People who think they have dysplastic nevi should point them out to the doctor. It is also important to tell the doctor about any new, changing, or “ugly-looking” moles.

Sometimes it is necessary to see a specialist. A dermatologist (skin doctor) is likely to have the most training in diseases of the skin. Some plastic surgeons, general surgeons, oncologists, internists, and family doctors also have a special interest and training in moles and melanoma.

Melanoma may run in families, and members of these families are at high risk for the disease. In some of these families, certain members also have a large number (usually over 100) of dysplastic nevi. These people have an especially high risk of developing melanoma. When two or more family members develop melanoma, it is important for all of the patients’ close relatives (parents, brothers, sisters, and children above the age of 10) to see a doctor and be examined carefully for dysplastic nevi or any signs of melanoma. The doctor can then decide how often each person needs to be seen. (Doctors may recommend that these family members have checkups every 6 months.) Anyone who has a large number of dysplastic nevi also should be examined regularly.

A doctor may want to watch a slightly abnormal mole closely to see whether it changes over time. Pictures taken at one visit may be compared with the appearance of the mole at the next visit. Sometimes a doctor decides that a mole should be removed so that the tissue can be examined under a microscope. The removal of a mole, called a biopsy, is usually done in the doctor’s office using a local anesthetic. It generally takes only a few minutes. The patient may require stitches, and a small scar will remain after healing. A pathologist examines the tissue under a microscope to see whether the melanocytes are normal, dysplastic, or cancerous.

Because most moles, including most dysplastic nevi, do not develop into melanoma, removing all of them is not necessary. A doctor can recommend when and when not to remove moles. Usually, only moles that look like melanoma, those that change, or those that are both new and look abnormal need to be removed.

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Other Booklets

The National Cancer Institute booklets listed below and others are available from the Cancer Information Service by calling 1-800-4-CANCER.

  • What You Need To Know About™ Cancer
  • What You Need To Know About™ Melanoma
  • What You Need To Know About™ Skin Cancer

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Pictures of Ordinary Moles and Dysplastic Nevi

Ordinary Moles Dysplastic Nevi
Color Evenly tan or brown; all typical moles on one person tend to look similar. Mixture of tan, brown, and red/pink. A person’s moles often look quite different from one another.
Shape Round or oval, with a distinct edge that separates the mole from the rest of the skin. Have irregular, sometimes notched edges. May fade into the skin around it. The flat portion of the mole may be level with the skin.
Surface Begin as flat, smooth spots on skin (1a); may become raised (1b) and form a smooth bump (1c). May have a smooth, slightly scaly, or rough, irregular, “pebbly” appearance.
Size Usually less than 5 millimeters (about 1/4 inch) across (size of a pencil eraser). Often larger than 5 millimeters (about 1/4 inch) across and sometimes larger than 10 millimeters (about 1/2 inch).
Number Between 10 and 40 typical moles may be present on an adult’s body. May be present in large numbers (more than 100 on the same person). However, some people have only a few dysplastic nevi.
Location Usually found above the waist on sun-exposed surfaces of the body. Scalp, breasts, and buttocks rarely have normal moles. May occur anywhere on the body but most frequently on the back and areas exposed to the sun. May also appear below the waist and on the scalp, breasts, and buttocks.

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Pictures of Melanoma

Large size Most melanomas are at least 5 millimeters (about 1/4 inch) across when they are found; many are much larger. An unusually large mole may be melanoma.
Many colors A mixture of tan, brown, white, pink, red, gray, blue, and especially blackin a mole suggests melanoma.
Irregular border If a mole has an edge that is irregular or notched, it may be melanoma.
Abnormal surface If a mole is scaly, flaky, oozing, or bleeding, has an open sore that does not heal, or has a hard lump in it, it may be melanoma.
Unusual sensation If a mole itches or is painful or tender, melanoma may be present.
Abnormal skin around mole If color from the mole spreads into the skin around it or if this skin becomes red or loses its color (becomes white or gray), melanoma may be present.