Melanoma, the most serious type of skin cancer, develops in the cells (melanocytes) that produce melanin — the pigment that gives your skin its color.
Melanoma can also form in your eyes and, rarely, in internal organs, such as your intestines.
The exact cause of all melanomas isn’t clear, but exposure to ultraviolet (UV) radiation from sunlight or tanning lamps and beds increases your risk of developing melanoma. Limiting your exposure to UV radiation can help reduce your risk of melanoma.
The risk of melanoma seems to be increasing in people under 40, especially women. Knowing the warning signs of skin cancer can help ensure that cancerous changes are detected and treated before the cancer has spread. Melanoma can be treated successfully if it is detected early.
Melanomas can develop anywhere on your body. They most often develop in areas that have had exposure to the sun, such as your back, legs, arms and face.
Melanomas can also occur in areas that don’t receive much sun exposure, such as the soles of your feet, palms of your hands and fingernail beds. These hidden melanomas are more common in people with darker skin.
The first melanoma signs and symptoms often are:
- A change in an existing mole
- The development of a new pigmented or unusual-looking growth on your skin
Melanoma doesn’t always begin as a mole. It can also occur on otherwise normal-appearing skin.
Normal moles are generally a uniform color — such as tan, brown or black — with a distinct border separating the mole from your surrounding skin. They’re oval or round and usually smaller than 1/4 inch (about 6 millimeters) in diameter — the size of a pencil eraser.
Most people have between 10 and 45 moles. Many of these develop by age 50, although moles may change in appearance over time — some may even disappear with age.
Unusual moles that may indicate melanoma
To help you identify characteristics of unusual moles that may indicate melanomas or other skin cancers, think of the letters ABCDE:
- A is for asymmetrical shape. Look for moles with irregular shapes, such as two very different-looking halves.
- B is for irregular border. Look for moles with irregular, notched or scalloped borders — characteristics of melanomas.
- C is for changes in colour. Look for growths that have many colours or an uneven distribution of colour.
- D is for diameter. Look for new growth in a mole larger than 1/4 inch (about 6 millimeters).
- E is for evolving. Look for changes over time, such as a mole that grows in size or that changes colour or shape. Moles may also evolve to develop new signs and symptoms, such as new itchiness or bleeding.
Cancerous (malignant) moles vary greatly in appearance. Some may show all of the changes listed above, while others may have only one or two unusual characteristics.
Melanomas can also develop in areas of your body that have little or no exposure to the sun, such as the spaces between your toes and on your palms, soles, scalp or genitals. These are sometimes referred to as hidden melanomas because they occur in places most people wouldn’t think to check. When melanoma occurs in people with darker skin, it’s more likely to occur in a hidden area.
Hidden melanomas include:
- Melanoma under a nail. Acral-lentiginous melanoma is a rare form of melanoma that can occur under a fingernail or toenail. It can also be found on the palms of the hands or the soles of the feet. It’s more common in blacks and in other people with darker skin pigment.
- Melanoma in the mouth, digestive tract, urinary tract or vagina. Mucosal melanoma develops in the mucous membrane that lines the nose, mouth, esophagus, anus, urinary tract and vagina. Mucosal melanomas are especially difficult to detect because they can easily be mistaken for other far more common conditions.
- Melanoma in the eye. Eye melanoma, also called ocular melanoma, most often occurs in the uvea – the layer beneath the white of the eye (sclera). An eye melanoma may cause vision changes and may be diagnosed during an eye exam.
Melanoma occurs when something goes awry in the melanin-producing cells (melanocytes) that give colour to your skin.
Normally, skin cells develop in a controlled and orderly way — healthy new cells push older cells toward your skin’s surface, where they die and eventually fall off. But when some cells develop DNA damage, new cells may begin to grow out of control and can eventually form a mass of cancerous cells.
Just what damages DNA in skin cells and how this leads to melanoma isn’t clear. It’s likely that a combination of factors, including environmental and genetic factors, causes melanoma. Still, doctors believe exposure to ultraviolet (UV) radiation from the sun and from tanning lamps and beds is the leading cause of melanoma.
UV light doesn’t cause all melanomas, especially those that occur in places on your body that don’t receive exposure to sunlight. This indicates that other factors may contribute to your risk of melanoma.