Innocent moles and the malignant variant

A birthmark is generally a light to dark brown colored spot that lies in or slightly on the skin. However, skin-colored, purple, red or blue birthmarks also occur. Occasionally the birthmark is already present at birth, but they usually appear between the ages of 3 and 40. On average, a person gets twenty moles in their lifetime. The vast majority of moles are and remain innocent. A birthmark (nevus naevocellularis) is a completely normal phenomenon that occurs in almost everyone to a greater or lesser extent. Birthmarks usually appear at a very young age and peak in number between the ages of 20 and 30. After the age of 70, the number often decreases spontaneously. A birthmark occurs when pigment cells, so-called melanocytes, clump together in the skin. The color of the birthmark depends on the number of pigment cells that clump together and the extent to which they can produce pigment. Birthmarks rarely occur on the palm of the hand and the sole of the foot. These spots contain much less pigment than other parts of the body. The chance that a normal, harmless mole will become malignant is approximately 1 in 1,000,000.

Common feature is innocent moles

An innocent birthmark / Source: Dbenbenn, Wikimedia Commons (CC BY-SA-3.0)

Birthmarks come in many different forms. Although most range in color from light to dark brown, moles in skin color, black, blue, purple and red are also not uncommon. A mole can lie completely in the skin and feel flat. But slightly raised rough spots or clearly visible and palpable bumps are also common. The dimensions of a birthmark vary from a few millimeters to several centimeters. Despite all these differences, harmless moles do have one common feature: both shape and color are uniform. The edges are generally sharply defined, the shape is almost symmetrical and there are no different colors in one mole. An exception to this is the ‘troubled birthmark’, which is more irregular in shape and has multiple color shades (for example several shades of brown to black and red).

The development of a birthmark

Why and how exactly a birthmark arises is largely unknown, apart from the fact that there is a clumping of pigment cells. The most important factor is probably heredity. Certain genes appear to play a major role in the development of moles. The relationship between exposure to UV rays (sunlight or tanning bed) or the number of times you have suffered a sunburn and the development of moles has not been clearly demonstrated. UV rays are harmful to the DNA in the skin and can cause skin cancer. However, the link between UV radiation and the development of melanoma (a malignant birthmark) is much less clear than that with other forms of skin cancer. No hard evidence has yet been provided regarding the influence of hormonal factors, such as long-term pill use or pregnancy, on the formation or discoloration of moles.

Special innocent birthmarks

Most moles are light to dark brown, evenly shaped, a maximum of a few millimeters in size and appear after the age of 3. However, a ‘congenital nevus’ is already present at or shortly after birth. Over time, hairs usually grow on this brown or black birthmark. A congenital mole can grow very large. A medium-sized mole has a size of 1.5 to 10 cm. A congenital giant birthmark can even cover more than a third of the body. About 1 in a hundred babies is born with a ‘congenital nevus’.
‘Spitz nevus’ is a fairly rare pink-red birthmark that mainly occurs in children. The birthmark is flat to spherical and has an average size of about 5 mm. A ‘Spitz nevus’ can grow quickly and is most common on the face and limbs. A ‘blue nevus’ is a blue-black birthmark that contains a lot of dark pigment and is partly deep in the skin. It is usually a round, small and firm bump that is smaller than 1 cm. The ‘blue nevus’ usually occurs in childhood and adolescence. The birthmark is commonly seen on the scalp, hands and feet. A ‘blue nevus’ is harmless, but because it is quite difficult to distinguish visually from a melanoma, it is often removed.

Halo nevus / Source: JeffyP, Wikimedia Commons (Public domain)

The ‘halo nevus’ is a birthmark with a light ring around it (a ‘halo’). In the light ring the pigment has disappeared from the skin. The cause is probably an autoimmune reaction, in which the body’s immune cells target the pigment cells at the site and clear them away. The birthmark itself is usually light to very dark brown. The light ring around the birthmark can sometimes be several centimeters wide . Often several ‘halo nevus’ are present on the body at the same time. A ‘Lentigo’ , also called a liver spot (because of its color) or age spot, is a benign pigmented abnormality of the skin. Strictly speaking, it is not a birthmark, but it is often classified as one. Eighty percent of white people over the age of 65 have at least one age spot. The lighter the skin, the more age spots. A clear link has been shown between the appearance of age spots and exposure to sunlight. It is a sign of skin aging and the more the skin comes into unprotected contact with UV rays, the more age spots appear. A ‘lentigo’ mainly occurs on the face, hands and forearms. It is a sharply defined spot that is round, oval or irregularly shaped. The color varies from uniform light to dark brown and the size from a few millimeters to a few centimeters.
An ‘atypical nevus’ or troubled birthmark is an irregular, irregularly shaped birthmark that is not sharply defined. The color varies from pink to brown and often multiple shades of color occur in one mole. A troubled mole is larger than 5 mm and sometimes has a slightly ulcerated edge. An ‘atypical nevus’ is harmless, but can occasionally be the precursor to melanoma.

The chance that an innocent mole will become malignant

A mole has a very small risk of becoming malignant. The chance that a melanoma will develop from the pigment cells of a normal mole is about 1 in a million. Melanoma is an aggressive form of skin cancer that unfortunately metastasizes quite quickly. With a congenital birthmark (congenital nevus) of 8 centimeters or more, the risk of a malignant change is greatest. A troubled mole (atypical nevus) ranks second in terms of the risk of developing melanoma. With the other moles the risk is very low.

Melanoma / Source: National Cancer Institute, Wikimedia Commons (Public domain)

When a mole develops into a malignant skin lesion, certain changes will occur. To assess this, an English mnemonic is often used: ‘ABCDE’ . The A stands for Asymmetry . If you divide the birthmark into two halves, one half should not look (very) different from the other half. The B stands for Border . The birthmark must be sharply defined in relation to normal skin. The edges of the birthmark should not become increasingly blurred. The birthmark should also not suddenly change shape (e.g. become irregular). The C stands for Colour . The color of the birthmark should be even and should not change suddenly. A melanoma often consists of different colors at the same time (brown, black, white, blue or red).
The D stands for Diameter (diameter). A mole that grows suddenly can be suspicious, especially if it becomes larger than 6 mm in diameter. However, if no other change can be seen or felt in the birthmark, the growth is almost always harmless. The E stands for Evolution (change). You need to keep an eye on a mole that suddenly changes in any way. Especially when the birthmark spontaneously bleeds, itches or hurts or when there are scabs or wounds on or in the birthmark.

Removing a birthmark

In most cases, changes in a birthmark have an innocent cause. However, it is absolutely wise to go to the doctor about this. This can usually visually determine (possibly with the help of a special viewer) whether there may be a malignant change. If melanoma is suspected, a biopsy is taken; a small piece of tissue is removed from the birthmark. A melanoma is surgically removed. Additional research is carried out to rule out metastases. If there are no metastases, the chance of recovery is extremely high.
An innocent birthmark does not need to be removed. However, if the mole is in an unpleasant spot, for example on your face or under your bra strap, you can usually have it removed quite easily. This can be done by your GP or dermatologist. Birthmarks on the skin are generally scraped off or burned away. Flat moles or moles about which there is any doubt are excised. The removed tissue can be sent to the pathologist for examination.
The chance that an innocent mole will turn into a malignant skin condition is very small. However, if you notice changes in your birthmark, especially in size or color, or if your birthmark spontaneously starts bleeding, stinging or itching, it is wise to go to the doctor. In the vast majority of cases, the changes have an innocent cause. However, it is very important to detect any melanoma early.

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