Moles (Nevi)

Overview

A mole, known medically as a nevus, is a common skin growth that forms when pigment-producing cells called melanocytes grow in a cluster rather than spreading evenly through the skin. Most moles are brown, tan, pink, or flesh-colored, and they can be flat or raised, smooth or slightly rough.

Most people have somewhere between 10 and 40 moles by adulthood. The majority appear during childhood and the teenage years, and they may darken with sun exposure, pregnancy, or hormonal changes. The vast majority of moles are completely harmless and stay the same for years. The main reason moles matter is that, in rare cases, a changing mole can be an early sign of skin cancer, so knowing what is normal for your skin is worthwhile.

Symptoms

A typical, healthy mole has predictable features:

• Round or oval with a smooth, even border
• One uniform color, usually brown, tan, or pink
• Smaller than about 6 millimeters (the size of a pencil eraser)
• Stable in size, shape, and color over time

Doctors use the ABCDE rule to flag moles that need attention: Asymmetry (one half unlike the other), Border that is irregular or blurred, Color that varies within the mole, Diameter larger than a pencil eraser, and Evolving (any change in size, shape, color, or new itching or bleeding). Any of these features is a reason to have the spot examined.

Causes

Moles form when melanocytes cluster together instead of dispersing through the skin. The exact trigger is not fully understood, but two main factors are involved:

• Genetics: The number and pattern of moles a person develops tends to run in families.
• Sun exposure: Ultraviolet (UV) light from the sun and tanning beds stimulates melanocytes and is linked to developing more moles and to changes in existing ones.

Hormonal shifts during the teenage years and pregnancy can also cause moles to appear, darken, or enlarge slightly. Some people are born with moles (congenital nevi), while most develop them over time (acquired nevi).

Risk Factors

Having a large number of moles, or unusual ones, is associated with a higher risk of skin cancer. Factors that raise concern include:

• More than 50 moles
• Fair skin, light hair, and a tendency to burn rather than tan
• A history of frequent or blistering sunburns
• Atypical (dysplastic) moles that look irregular
• A personal or family history of melanoma

Diagnosis

A doctor or dermatologist can usually evaluate a mole by examining the skin. Helpful steps include:

• Visual skin exam: Checking the size, shape, color, and texture, often with a handheld magnifier called a dermatoscope.
• Comparison over time: Photographs may be used to track moles that need monitoring.
• Biopsy: If a mole looks suspicious, a small sample or the whole mole is removed and examined under a microscope to rule out skin cancer.

A biopsy is the only way to know for certain whether a worrying mole is cancerous.

Treatment

Normal moles need no treatment. A mole may be removed if it is suspicious, irritated by clothing or shaving, or for cosmetic reasons. Removal options include:

• Surgical excision: The mole is cut out and the skin closed with stitches; this is standard when cancer must be ruled out.
• Shave removal: A raised mole is shaved level with the skin using a small blade.

Any removed tissue from a concerning mole should be sent to a laboratory. Be cautious of over-the-counter mole-removal creams or attempts to remove moles at home, which can cause scarring, infection, and may leave cancer undiagnosed.

Prevention

You cannot prevent moles entirely, but protecting your skin lowers the risk of new moles and of skin cancer:

• Use broad-spectrum sunscreen of SPF 30 or higher
• Seek shade during peak midday sun and wear protective clothing and a hat
• Avoid tanning beds
• Examine your own skin regularly and note any new or changing spots
• See a dermatologist for periodic skin checks if you have many moles or a family history of melanoma

When to See a Doctor

Have a mole checked promptly if it shows any of the ABCDE warning signs, or if it:

• Itches, bleeds, crusts, or becomes painful
• Grows or changes color noticeably
• Appears newly after age 30
• Looks different from your other moles (the "ugly duckling" sign)

Early evaluation of a changing mole is the best way to catch skin cancer when it is most treatable. When in doubt, get it looked at.

Related Topics

Frequently Asked Questions

References

1. American Academy of Dermatology. Moles: Signs and symptoms.
2. Mayo Clinic. Moles — Symptoms and causes.
3. National Cancer Institute. Common Moles, Dysplastic Nevi, and Risk of Melanoma.
4. MedlinePlus, U.S. National Library of Medicine. Moles.