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

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 color. Look for growths that have many colors or an uneven distribution of color.
• 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 color 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.

Hidden melanomas

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 black people 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 color 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.

Factors that may increase your risk of melanoma include:

• Fair skin. Having less pigment (melanin) in your skin means you have less protection from damaging UV radiation. If you have blond or red hair, light-colored eyes, and freckle or sunburn easily, you're more likely to develop melanoma than is someone with a darker complexion. But melanoma can develop in people with darker complexions, including Hispanic people and black people.
• A history of sunburn. One or more severe, blistering sunburns can increase your risk of melanoma.
• Excessive ultraviolet (UV) light exposure. Exposure to UV radiation, which comes from the sun and from tanning lights and beds, can increase the risk of skin cancer, including melanoma.
• Living closer to the equator or at a higher elevation. People living closer to the earth's equator, where the sun's rays are more direct, experience higher amounts of UV radiation than do those living in higher latitudes. In addition, if you live at a high elevation, you're exposed to more UV radiation.
• Having many moles or unusual moles. Having more than 50 ordinary moles on your body indicates an increased risk of melanoma. Also, having an unusual type of mole increases the risk of melanoma. Known medically as dysplastic nevi, these tend to be larger than normal moles and have irregular borders and a mixture of colors.
• A family history of melanoma. If a close relative — such as a parent, child or sibling — has had melanoma, you have a greater chance of developing a melanoma, too.
• Weakened immune system. People with weakened immune systems, such as those who've undergone organ transplants, have an increased risk of skin cancer.