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Moles (acquired nevi)

What is a mole?

A mole, or nevus, is a very common skin growth that occurs when skin colour cells, known as melanocytes, build up under the surface of the skin. Moles vary in size, colour and appearance and can also change over time. They are usually round, but they may also have an oval or jagged shape. Their colour ranges from pinkish red or light brown to dark brown or black.

Healthy and benign moles

Moles can be flat, bumpy or verrucous (like a wart). They usually occur in body parts that are frequently exposed to the sun, but they can be found anywhere, even inside the mouth, eyes and genitals.

Moles fall into two main groups:

  • congenital melanocytic nevi – moles that your child has at birth or are noticed shortly after birth
  • acquired nevi – moles that develop later in life.

What causes moles to appear?

Several factors can cause moles to appear:

  • sun exposure (more time in the sun increases the number of moles on your skin)
  • higher levels of cortisone, corticotropin and other hormones that help the body grow
  • chemotherapy (medication that treats cancer)
  • immunosuppression (a weakened immune system that prevents the body from fighting infections).

How do moles affect the body?

Moles are usually benign (harmless), but they can sometimes change and become skin cancer (melanoma). This can be very serious and sometimes lead to death if not treated in time.

Benign moles

A benign mole has the following three features.

  • It is symmetrical – you can draw an imaginary line and divide it into two identical pieces.
  • It has a regular border – there is a clear difference between the colour of the mole and skin around it.
  • It has a uniform pigment – every area of the mole is the same colour.

In general, benign moles:

  • grow as your child grows, becoming bigger as the skin stretches
  • get darker or lighter with time
  • may sometimes have coarse hair growing from them
  • will normally change a little throughout life, for example become raised over several years.

Potentially harmful moles

A mole that is potentially harmful might:

  • change shape
  • rapidly grow (out of proportion with the child’s growth)
  • develop an uneven colour
  • form a scab or bleed without any injury.

A dermatologist (skin specialist) should examine your child’s skin if it looks different than it used to, if an area opens up, bleeds and has a hard time healing or if a new mole suddenly appears.

How is a potentially harmful mole diagnosed?

Dermatologists and other healthcare professionals use the letters “ABCDE" as a guide when checking the skin for potentially harmful changes in existing or new moles. You can also use this guide when checking your child’s skin at home.

  • A stands for asymmetry (having two sides or halves that are not the same)
  • B stands for border irregularity (the borders of the mole are not well defined)
  • C stands for colour variation (different colour tones in the same mole, for example light and dark brown)
  • D stands for diameter larger than 6 mm
  • E stands for evolving (including any dramatic change in shape, colour or appearance in existing moles)

If a mole has any of these characteristics, it should be examined more closely. A dermatoscopic examination (examining the skin using a special magnifying glass) or a skin biopsy​ (examining a small sample of the mole’s cells under a microscope) can tell your dermatologist or doctor if the mole is benign or malignant.

ABCDEs of potentially harmful moles

How can I or my child inspect my child’s skin at home?

  1. Do the inspection in a well-lit area.
  2. If you are inspecting your child’s skin, gather a hair dryer, two chairs or stools, a camera or smartphone, a ruler and a pen and paper. If your child is inspecting their own skin, they will need these tools and two mirrors, one that is hand-held mirror and one hanging on a wall or a door.
  3. Inspect the different parts of the body in the same order each time. For example, always work from the head down or the feet up.
  4. If working down from the head, for example, start by parting your child’s hair with a hair dryer or your hands to check their scalp. This is easier to do when the hair is wet.
  5. Check your child’s shoulders, chest and genital area.
  6. Check the back of their shoulders, their upper and lower back and their buttocks.
  7. Check their upper arms, elbows, forearms, wrists, hands, palms and fingers, including the space between their fingers.
  8. Check their inner and outer legs, front and back, including their knees and ankles.
  9. Check their feet and toes, including the soles and the space between the toes.
  10. Take a photo of any moles with a ruler beside them so you can record the size and keep track of any changes over time.

Can children develop melanoma?

Yes they can, although melanoma in children is very rare. Only one child in one million children below age 15 develops melanoma.

The risk factors for developing melanoma during childhood include:

  • having dysplastic nevi (irregular looking moles)
  • having a close family member, such as a parent or grandparent, with a history of melanoma
  • having a large number (more than 100) of melanocytic nevi, or moles
  • being immunosuppressed or having inherited immunodeficiency (weakened immune system) 
  • having a sun-sensitive phenotype (very fair skin, light coloured eyes and red or light hair)
  • being exposed to ultraviolet radiation from the sun
  • having a history of malignancy (any form of cancer)
  • having a genetic disorder that makes the skin more sensitive to sun damage (for example xeroderma pigmentosum).

What can I do to reduce the risk of melanoma?

  • Avoid too much sun exposure (use a hat and special SPF clothing at the beach or in sunny places).
  • Do not let your child or teenager use tanning beds​.
  • Use sunscreen (SPF 30 or higher, covering both UVA and UVB rays) every day, even during winter months, and reapply it periodically during the day.
  • Check the skin using the ABCDE acronym at least once every six months.
  • Talk to your child’s doctor if you notice any change that concerns you.

Key points

  • Moles occur when there is a build-up of melanocytes under the skin. This can happen as a result of sun exposure, high levels of growth hormones or chemotherapy.
  • Most moles are benign. They are symmetrical and have a regular border and even pigment throughout.
  • The ABCDE acronym can help you, your child or a dermatologist identify any potentially harmful moles.
  • To reduce the risk of harmful moles (melanoma), avoid too much sun exposure, use sunscreen and check your child’s skin at least once every six months.

Blanca DelPozzo-Magana, MD
Irene Lara-Corrales​, MSc, MD