Moles are a common type of skin growth. They often appear as small, dark brown spots and are caused by clusters of pigmented cells. Moles generally appear during childhood and adolescence. Most people have 10 to 40 moles, some of which may change in appearance or fade away over time.

Most moles are harmless. Rarely, they become cancerous. Monitoring moles and other pigmented patches is an important step in detecting skin cancer, especially malignant melanoma.

The medical term for moles is nevi.

The typical mole is a brown spot. But moles come in different colors, shapes and sizes:

• Color and texture. Moles can be brown, tan, black, red, blue or pink. They can be smooth, wrinkled, flat or raised. They may have hair growing from them.
• Shape. Most moles are oval or round.
• Size. Moles are usually less than 1/4 inch (about 6 millimeters) in diameter — the size of a pencil eraser. Rarely, moles present at birth (congenital nevi) can be much bigger, covering wide areas of the face, torso or a limb.

Moles can develop anywhere on your body, including your scalp, armpits, under your nails, and between your fingers and toes. Most people have 10 to 40 moles. Many of these develop by age 50. Moles may change in appearance or fade away over time. Hormonal changes of adolescence and pregnancy may cause moles to become darker and larger.

Unusual moles that may indicate melanoma

This ABCDE guide can help you determine if a mole or a spot may indicate melanoma or other skin cancers:

• A is for asymmetrical shape. One half is unlike the other half.
• B is for border. Look for moles with irregular, notched or scalloped borders.
• C is for color. Look for growths that have changed color, have many colors or have uneven color.
• D is for diameter. Look for new growth in a mole larger than 1/4 inch (about 6 millimeters).
• E is for evolving. Watch for moles that change in size, shape, color or height, especially if part or all of a mole turns black. Moles may also evolve to develop new signs and symptoms, such as itchiness or bleeding.

Cancerous (malignant) moles vary greatly in appearance. Some may show all of the features listed above. Others may have only one or two.

When to see a doctor

Make an appointment with your doctor if a mole looks unusual, grows or changes.

Moles are caused when cells in the skin (melanocytes) grow in clusters or clumps. Melanocytes are distributed throughout your skin and produce melanin, the natural pigment that gives your skin its color.

Melanoma is the main complication of moles. Some people have a higher than average risk of their moles becoming cancerous and developing into melanoma. Factors that increase your risk of melanoma include:

• Being born with large moles. These types of moles are called congenital nevi. On an infant, such moles are classified as large if they're more than 2 inches (5 centimeters) in diameter. Even a large mole seldom becomes cancerous and almost never before the child reaches puberty.
• Having unusual moles. Moles that are bigger than a common mole and irregular in shape are known as atypical (dysplastic) nevi. They tend to be hereditary. And they often have dark brown centers and lighter, uneven borders.
• Having many moles. Having more than 50 ordinary moles indicates an increased risk of melanoma. Two studies add to the evidence that the number of your moles predict cancer risk. One showed that people under 50 years old who have 20 or more moles on their arms are at increased risk of melanoma. Another showed a relationship between the number of women's moles and breast cancer risk.
• Having a personal or family history of melanoma. If you've had melanoma before, you are at increased risk of a mole becoming cancerous. In addition, some types of atypical moles lead to a genetic form of melanoma.

The following measures can help limit the development of moles and the main complication of moles — melanoma.

Watch for changes

Become familiar with the location and pattern of your moles. Regularly examine your skin to look for changes that may signal melanoma. Do self-exams once a month, especially if you have a family history of melanoma. With the help of mirrors, do a head-to-toe check, including your scalp, palms and fingernails, armpits, chest, legs, and your feet, including the soles and the spaces between the toes. Also check your genital area and between your buttocks.

Talk with your doctor about your risk factors for melanoma and whether you need a professional skin exam on a routine basis.

Protect your skin

Take measures to protect your skin from ultraviolet (UV) radiation, such as from the sun or tanning beds. UV radiation has been linked to increased melanoma risk. And children who haven't been protected from sun exposure tend to develop more moles.

• Avoid peak sun times. For many people in North America, the sun's rays are strongest between 10 a.m. and 4 p.m. Schedule outdoor activities for other times of the day, even on cloudy days or in winter.
• Use sunscreen year-round. Apply sunscreen about 30 minutes before going outdoors, even on cloudy days. Use a broad-spectrum sunscreen with an SPF of at least 15. Apply it generously and reapply every two hours — or more often if you're swimming or sweating. The American Academy of Dermatology recommends using a broad-spectrum, water-resistant sunscreen with an SPF of at least 30.
• Cover up. Sunglasses, broad-brimmed hats, long sleeves and other protective clothing 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.
• Avoid tanning lamps and beds. Tanning lamps and beds emit UV rays and can increase your risk of skin cancer.

Your doctor can identify moles by looking at your skin. 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. During a skin exam, your doctor inspects your skin from head to toe.

If your doctor suspects that a mole may be cancerous, he or she may take a tissue sample (biopsy) for microscopic examination.

Most moles don't need treatment.

Mole removal

If your mole is cancerous, your doctor will do a surgical procedure to remove it. If you have a mole that causes irritation when you shave, you may want to have it removed.

Mole removal takes only a short time and is usually done on an outpatient basis. Your doctor numbs the area around the mole and cuts it out, along with a margin of healthy skin if necessary. The procedure may leave a permanent scar.

If you notice that a mole has grown back, see your doctor promptly.

Cosmetic care

If you're self-conscious about a mole, you could try makeup to help conceal it. If you have a hair growing from a mole, you might try clipping it close to the skin's surface or plucking it. Or talk with your dermatologist about permanently removing the hair and the mole.

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

If you have a mole that concerns you, your family doctor can usually let you know if it's normal or needs further investigation. He or she may then refer you to a doctor who specializes in skin disorders (dermatologist) for diagnosis and treatment.

It's a good idea to arrive for your appointment well-prepared. Here's some information to help you get ready.

What you can do

• List any changes you've noticed or any new symptoms you're experiencing. Include any that may seem unrelated to the reason for which you scheduled the appointment.
• Bring a list of all medications, vitamins or supplements that you're taking.
• If you've had a melanoma or a mole removed in the past, note the location of the lesion and the date of removal. If you have the biopsy report, bring it with you.
• Don't wear makeup or opaque nail polish to your appointment. These products make it difficult for your doctor to perform a thorough exam.
• List questions to ask your doctor.

For moles, some basic questions to ask your doctor include:

• Do you think this mole might be cancerous?
• What's the most appropriate course of action?
• How can I tell if a mole needs to be looked at?
• Can I prevent more moles from developing?
• Do you have any brochures or other printed material that I can take home with me? What websites do you recommend?

In addition to the questions that you've prepared, don't hesitate to ask questions during your appointment.

What to expect from your doctor

Your doctor is likely to ask you a number of questions, such as:

• When did you first notice this mole?
• Have you always had it, or is it new?
• Have you noticed any changes in this mole, such as its color or shape?
• Have you had other moles surgically removed in the past? If so, do you know if they were unusual (atypical) or malignant?
• Do you have a family history of atypical moles, melanoma or other cancers?
• Have you had peeling sunburns or frequent exposure to ultraviolet radiation, such as from tanning beds?