A melanoma is a malignant tumor that originates in melanocytes, which are cells responsible for generating melanin (pigment that gives color to skin, hair and eyes and is strongest in moles). Melanomas, therefore, are generally brown or black. Sometimes, melanomas stop generating pigment. In such cases, the melanomas are red, pink, purple or skin-colored.

Melanomas can be in situ or invasive. In situ in Latin means "localized." These types of melanomas occupy only the top layer of the skin. Invasive melanomas are far more serious and difficult to cure. They go much deeper into the skin, having traveled through the body.

Melanomas are divided into four broad groups. Three start in situ and later become invasive; the fourth form of melanoma is invasive from the beginning.

Superficial spreading melanoma is the most prevalent type of melanoma. 70% of all reported cases are superficial spreading melanoma. This melanoma occupies the top layer of the skin for a long time before being invasive. Melanomas affecting the younger age group are normally the superficial type.

Lentigo maligna is similar, in that it also affects the top layer of the skin for a long time before going deeper. The older age group is mostly affected by this type of melanoma. This condition can take place in the ears, arms and upper trunk, if they have been constantly exposed to the sun. Lentigo maligna melanoma is considered to be an invasive form of the disease.

Acral lentiginous melanoma is the third form of melanoma, and like the first two it spreads along the top surface before tuning invasive. Acral lentiginous melanoma is sometimes found in people of darker skin. It is more prevalent among Asians and African-Americans than Caucasians.

Nodular melanoma, the fourth type of melanoma, is easily the most aggressive. It is invasive at the time of diagnosis. The most commonly affected areas are arms, legs, trunks (especially of older people) and the scalp. Nodular melanoma constitutes 10% to 15% of all melanoma cases.

Malignant melanomas are typified by brown, black or big bright patches, and nodules with uneven outline. They sit on top of the skin surface or bleed. Mostly, they originate in already existing moles. Melanoma generally targets the trunk in men. In women, arms and lower legs are affected.

Melanoma is known to be genetic as well. In some families, people have "dysplastic nevi" or strange-looking moles that are more liable to turn cancerous than others. It is imperative for those people to have regular checkups for detection of cancerous cells.