Melanoma, also called cutaneous melanoma, is the most serious type of skin cancer. It happens when melanocytes, the cells that give your skin its color, become damaged and grow out of control. Unlike other types of skin cancer, it can spread quickly to other parts of the body. There are three types of cells that make up the top layer of your skin, known as the epidermis: squamous cells, basal cells and melanocytes. Squamous cell carcinoma is cancer on the top layer of the skin. It usually occurs in areas of your body that get the most sun. It can metastasize, or spread, to other parts of your body. Basal cell carcinoma is the most common type of skin cancer. It grows slowly and doesn’t tend to spread to other areas. Melanocytes are the bottom layer and, in addition to making melanin, the substance in your body that produces hair, eye and skin color, it also helps protect the deeper layers of skin from the sun’s ultraviolet (UV) radiation. There are four types of melanoma:Superficial spreading melanoma: The most common form, typically found on the legs and upper back in women. It usually looks flat and discolored. Lentigo maligna melanoma: Typically appears in older adults and looks similar to the superficial spreading form, appearing flat with blotchy patches of blue-black, tan or brown.Acral lentiginous melanoma: The most common melanoma in people of color, appearing black or brown in color. It can develop under the nails, on the palms or on the soles of the feet. Nodular melanoma: This is the most aggressive form of melanoma and it tends to grow quickly. Appears as a bump, reddish or blue-black in color. Researchers aren’t exactly sure how melanoma forms, but genetics and environment might play a role. Exposure to UV rays from the sun or tanning beds increases your risk of developing melanoma.