Moles are very common, and most people have one or more. Moles are concentrations of pigment-producing cells (melanocytes) in your skin. People with light skin tend to have more moles.

The technical name for a mole is nevus (plural: nevi). It comes from the Latin word for birthmark.

The cause of moles isn’t well understood. It’s thought to be an interaction of genetic factors and sun damage in most cases.

Moles usually emerge in childhood and adolescence, and change in size and color as you grow. New moles commonly appear at times when your hormone levels change, such as during pregnancy.

Most moles are less than 1/4 inch in diameter. Mole color ranges from pink to dark brown or black. They can be anywhere on your body, alone or in groups.

Almost all moles are benign (noncancerous). But new moles in an adult are more likely to become cancerous than old moles.

If a new mole appears when you're older, or if a mole changes in appearance, you should see a dermatologist to make sure it’s not cancerous.

There are many types of moles, categorized by when they appear, what they look like, and their risk of becoming cancerous.

Congenital moles

These moles are called birthmarks and vary widely in size, shape, and color. About 0.2 to 2.1 percent of infants are born with a congenital mole.

Some birthmarks may be treated for cosmetic reasons when the child is older, for example, age 10 to 12 and better able to tolerate local anesthetic. Treatment options include:

  • surgery
  • skin resurfacing (dermabrasion)
  • skin shaving (excision) of top skin layers
  • chemical peel for lightening
  • laser ablation for lightening

Risk

Larger congenital moles have a greater risk of becoming malignant in adulthood (4 to 6 percent lifetime risk). Changes in growth, color, shape, or pain of a birthmark should be evaluated by a doctor.

Acquired moles (also called common moles)

Acquired moles are those that appear on your skin after you’re born. They’re also known as common moles. They can appear anywhere on your skin.

People with fair skin can normally have between 10 and 40 of these moles.

Common moles are usually:

  • round or oval
  • flat or slightly raised or sometimes dome-shaped
  • smooth or rough
  • one color (tan, brown, black, red, pink, blue, or skin-colored)
  • unchanging
  • small (1/4 inch or less; the size of a pencil eraser)
  • may have hairs

If you have darker skin or dark hair, your moles may be darker than those of people with fairer skin.

Risk

If you have more than 50 common moles, you’re at a higher risk for skin cancer. But it’s rare for a common mole to become cancerous.

Atypical moles (also called dysplastic nevi)

Atypical moles can appear anywhere on your body. Atypical moles are often on the trunk, but you can also get them on your neck, head, or scalp. They rarely appear on the face.

Benign atypical moles may have some of the same characteristics as melanoma (a type of skin cancer). So, it’s important to have regular skin checks and to monitor any changes in your moles.

Atypical moles have the potential to become cancerous. But it’s estimated that only 1 in 10,000 atypical moles turn into cancer.

Because of their appearance, atypical moles have been characterized as the “ugly ducklings” of moles.

In general, atypical moles are:

  • irregular in shape with uneven borders
  • varied in color: mixes of tan, brown, red, and pink
  • pebbled in texture
  • larger than a pencil eraser; 6 millimeters or more
  • more common in fair-skinned people
  • more common in people who have high sun exposure

Risk

You have a higher risk of getting melanoma if you have:

  • four or more atypical moles
  • a blood relative who had melanoma
  • previously had melanoma

If members of your family have a lot of atypical moles, you may have familial atypical multiple mole melanoma (FAMMM) syndrome. Your risk of melanoma is 17.3 times higher that people who don't have FAMMM syndrome.

The cause of a new mole that appears in adulthood isn’t well understood. New moles may be benign or they may be cancerous. Melanoma causes are well studied, but there’s little research on what causes benign moles.

Genetic mutations are likely involved. A 2015 research study reported that genetic mutations of the BRAF gene were present in 78 percent of benign acquired moles.

BRAF mutations are known to be involved in melanoma. But the molecular processes involved in transforming a benign mole to a cancerous mole aren’t yet known.

The interaction of ultraviolet light (UV), both natural and artificial, with DNA is known to cause genetic damage that can lead to the development of melanoma and other skin cancers. The sun exposure can occur during childhood or young adulthood and only much later result in skin cancer.

Reasons that you may have a new mole include:

  • increasing age
  • fair skin and light or red hair
  • family history of atypical moles
  • response to drugs that suppress your immune system
  • response to other drugs, such as some antibiotics, hormones, or antidepressants
  • genetic mutations
  • sunburn, sun exposure, or tanning bed use

New moles are more likely to become cancerous. A 2017 review of case studies found that 70.9 percent of melanomas arose from a new mole. If you’re an adult with a new mole, it’s important to have it checked by your doctor or a dermatologist.

When an old mole changes, or when a new mole appears in adulthood, you should see a doctor to check it out.

If your mole is itching, bleeding, oozing, or painful, see a doctor right away.

Melanoma is the deadliest skin cancer, but new moles or spots may also be basal cell or squamous cell cancers. These usually appear in areas that are exposed to the sun, such as your face, head, and neck. They’re easily treatable.

Melanomas

Here's an ABCDE melanoma guide about what to look for, developed by the American Academy of Dermatology:

  • Asymmetrical shape. Each half of the mole is different.
  • Border. The mole has irregular borders.
  • Color. The mole has changed color or has many or mixed colors.
  • Diameter. The mole gets larger — more than 1/4 inch in diameter.
  • Evolving. The mole keeps changing in size, color, shape, or thickness.

Skin self-checks

Checking your skin regularly can help you spot mole changes. More than half of skin cancers occur on parts of your body that you can easily see.

It’s uncommon to find melanomas in parts of the body protected from the sun. The most common body sites for melanoma in women are the arms and legs.

For men, the most common melanoma sites are the back, trunk, head and neck.

Non-Caucasians have a lower risk for melanoma in general. But the melanoma locations are different for people of color. Typical sites for melanoma among non-Caucasians are:

  • the soles
  • the palms
  • in between toes and fingers
  • under toenails or fingernails

Note that self-checks can often miss changes in moles, according to a 2000 study of people at high risk for melanoma.

Moles that appear in adulthood should always be checked by a doctor. It’s recommended that people have a skin check by a dermatologist yearly. If you’re at risk for melanoma, your doctor may recommend a skin check every six months.

If you have a mole that changes, especially one that meets one or more of the criteria in the ABCDE guide above, see a doctor right away.

The good news is that early detection of melanoma leads to significant survival benefits. The 10-year survival rate for melanoma that is detected early is 93 percent.