What is Melanoma?

Melanoma is a cancer of the skin that begins in melanocytes, the cells responsible for producing melanin, the pigment that gives skin, hair, and eyes their color. It develops when melanocytes begin to grow and divide in an uncontrolled way, most often in skin that has been exposed to the sun. While the majority of melanomas arise on the skin — known as cutaneous melanoma — the disease can also develop in other pigmented tissue, including the eye (ocular melanoma) and the mucous membranes lining the digestive tract, mouth, or genitals (mucosal melanoma).

Melanoma accounts for a relatively small share of all skin cancer diagnoses, but it's considered the most serious type because it's far more likely than basal cell or squamous cell skin cancers to invade nearby tissue and spread, or metastasize, to the lymph nodes and other organs. Early lesions tend to grow along the surface of the skin before penetrating into deeper layers, which is why a change in an existing mole or a new, unusual growth is an important early warning sign. Once diagnosed, melanoma is staged based on factors such as tumor thickness and the presence of ulceration; prognosis and treatment depend heavily on how early the disease is caught, since localized melanoma is highly treatable while spread to distant organs is more difficult to manage.

Types of Skin Melanoma

There are four main types of skin melanoma, distinguished by how and where they develop:

• Superficial Spreading Melanoma: The most common type, it grows outward across the surface of the skin before growing deeper. It can start in an existing mole, though many cases arise on normal-looking skin.
• Nodular Melanoma: Appears as a raised nodule on the skin that is often brown or black. This type tends to grow into deeper layers of skin early, so it's often found at a more advanced stage.
• Lentigo Maligna Melanoma: Occurs most often in older adults. This type appears as an abnormally shaped, discolored spot in an area that receives significant sun exposure and tends to grow slowly over time.
• Acral Lentiginous Melanoma: Starts in areas that receive less sun exposure than other parts of the body, such as the palms, soles, or under the nails.

Accurate identification of subtype, along with tumor thickness and depth of growth, helps guide diagnosis, staging, and treatment planning.

Risk Factors for Melanoma

A risk factor is any characteristic or exposure that increases the likelihood of developing a disease. While not all individuals with these risk factors will develop melanoma, understanding them can inform prevention and early detection strategies.

• Family History: A family history of melanoma increases the likelihood of developing the disease.
• History of Sunburn: One or more severe sunburns, particularly during childhood, is associated with increased risk later in life.
• Exposure to UV Light: Cumulative exposure to ultraviolet radiation, from the sun or from tanning beds and lamps, damages the DNA in skin cells and is the leading environmental cause of melanoma.
• Atypical Moles: Having numerous moles, or moles that are unusually large, irregular in shape, or atypical in appearance, raises the risk of melanoma.
• Geography: Living closer to the equator or at a higher elevation increases exposure to UV radiation and, with it, the risk of melanoma.
• Skin That Sunburns Easily: Fair skin, along with light-colored hair or eyes, is associated with higher risk due to lower natural protection from UV damage.
• Weakened Immune System: A weakened immune system, whether from a medical condition or immunosuppressive medication, can increase susceptibility to melanoma.

The presence of multiple risk factors may have a cumulative effect, though melanoma can also develop in people without any of the recognized risk factors above.

Reducing the Risk of Melanoma

While there's no way to eliminate melanoma risk entirely, several habits can help reduce UV-related skin damage and support early detection:

• Avoid Tanning Lamps and Beds: Artificial UV light from tanning devices carries many of the same risks as sun exposure.
• Avoid the Sun During Midday: UV rays are strongest in the middle of the day; seeking shade during these hours reduces cumulative exposure.
• Watch for Changes in the Skin: Regularly checking the skin for new growths or changes in existing moles supports early detection.
• Wear Protective Clothing: Clothing that covers the skin, along with wide-brimmed hats and sunglasses, helps block UV exposure.
• Use Sunscreen Regularly: Applying broad-spectrum sunscreen, and reapplying it regularly, reduces UV-related skin damage.

Sources: National Cancer Institute (cancer.gov), American Cancer Society (cancer.org), and Mayo Clinic