The UV rays from the sun can cause significant skin damage. UV rays penetrate the skin's outer layers and reach the deeper layers, where they can harm or kill skin cells. People, especially those with little melanin and those who burn easily, should take precautions. The more skin that is exposed to sunlight, the greater the risk of cancer development. Skin cancers are common and often deadly. They are the most common type of cancer in the United States. There are several types of skin cancers including melanoma, which develops from pigment-producing skin cells called melanocytes. Other types of skin cancers include basal cell carcinoma and squamous cell carcinoma. Basal cell carcinomas do not spread but can become large and visible if left untreated. Squamous cell carcinomas usually start as small papules on the skin's surface and may develop into larger tumors. They are likely to spread to other parts of the body where they can cause death. Deaths from skin cancer are generally caused by complications such as metastasis (spread of the cancer tumor cells) or infection. Cancer deaths could also be caused by other factors such as malnutrition or medical errors. Some people have life-threatening reactions to the drugs used to treat cancer; these reactions are mostly allergic reactions resulting from a body's own defense mechanism. Life-threatening effects include anaphylaxis, a severe reaction that can lead to death.