Skin cancer is the most common form of cancer in the U.S., with one in five Americans likely to be diagnosed at some point during his or her lifetime. Skin cancer can develop when certain skin cells change and start to grow abnormally.
How dangerous a skin cancer is likely to be depends on what type it is, as well as how far it has spread. Here's what to know about the three main types of skin cancer:
Basal cell carcinoma (BCC)
How common: Causes roughly 77 percent of skin cancers, with an estimated 2.8 million diagnosed every year.
How dangerous: Basal cell carcinomas tend to be slow growing and not very dangerous; they only rarely spread to other parts of the body. However, given enough time, a basal cell carcinoma can invade the surrounding tissue and damage cartilage or even bone.
What it looks like: Usually looks like a shiny, slow-growing bump or nodule on the skin. Basal cell carcinomas usually grow in areas exposed to the sun.
Squamous cell carcinoma (SCC)
How common: Causes roughly 20 percent of skin cancers, with an estimated 700,000 diagnosed yearly.
How dangerous: Squamous cell carcinomas are highly treatable but can be dangerous if they grow quickly or if they're allowed to spread. An estimated 1 to 5 percent of squamous cell carcinomas metastasize, causing about 2,500 deaths every year.
What it looks like: Squamous cell carcinomas may look like red or flesh-colored nodules or like red scaly patches of skin. An estimated 60 percent of squamous cell carcinomas develop in preexisting actinic keratoses (a common sun-related precancerous skin lesion). They're commonly found in sun-exposed areas, such as the arms or neck, but they sometimes develop in non-sun-exposed areas, such as in a preexisting scar or burn. They also sometimes develop in the mouth or lip, especially in people who smoke or use tobacco.
How common: Causes only 3 to 4 percent of skin cancers, with an estimated 124,000 diagnosed yearly.
How dangerous: Melanomas are by far the most dangerous type of skin cancer. Although many diagnosed melanomas are superficial and quite treatable, melanomas often become invasive and metastatic. These cause the majority of skin cancer deaths (about 8,800 deaths in 2011).
What it looks like: Melanomas start in melanocytes, which are the pigment cells in the skin, so most melanomas look like abnormal moles, and many develop in a preexisting mole. Some melanomas may look like a large, spreading freckle. Melanomas can develop on sun-exposed skin or may develop on other parts of the body.
If you're worried about possible skin cancer, see 6 Signs to See a Doctor About Possible Skin Cancer and 4 Steps to a Skin Cancer Diagnosis.