An irregular mole, a sore that doesn’t heal and other changes can signal melanoma. (Marvin Joseph/The Washington Post)

What is skin cancer?

There are three main types:

Melanoma: the most deadly.

Squamous cell and basal cell: the most common in humans, the slowest-growing and also the easiest to treat.

In African Americans, squamous cell carcinomas occur mainly on the legs and genital area, and sometimes arise from scarring or chronic inflammation, according to the Skin Cancer Foundation. They can be more aggressive and dangerous for African Americans than for whites, due in part to later detection and treatment. Smoking and infection with human papillomavirus are risk factors, according to Ali Hendi, a spokesman for the foundation.

A patient gets a skin exam from a dermatologist during a follow up visit after a melanoma removal in 2009. (T.J. Kirkpatrick for The Washington Post)

For Caucasians, sun exposure is the greatest risk factor for all types of skin cancers. Although dark-skinned individuals enjoy greater protection than whites, they are not immune.

What are the warning signs?

The American Cancer Society offers these “ABCDE” warning signs of melanoma, which can appear on the skin as a mole, lesion or spot:

Asymmetry: One half of a mole doesn’t match the other half.

Border: The border is irregular, notched, blurred or ragged.

One of the best known benefits of sunlight is its ability to boost the body's vitamin D supply, but what happens when you can't get outside in the sun? George Washington University's Dr. Michael Irwig explains how sunlight, or lack of it, can affect a person's health. (Pamela Kirkland, Gillian Brockell, and Kate M. Tobey/The Washington Post)

Color: The mole or lesion has a variety of colors, including shades of brown, tan or black, sometimes with patches of pink, red, white or blue.

Diameter: The suspicious area is new or at least a quarter-inch in diameter (the size of a pencil eraser).

Evolving: The mole is changing in size, shape or color.

Other warning signs:

● A sore that does not heal.

● Spread of pigment from the border of a spot to surrounding skin.

● Redness or a new swelling beyond the border.

● Change in sensation: itchiness, tenderness or pain.

● Change in the surface of a mole: scaliness, oozing, bleeding or the appearance of a bump or nodule.

For people of color, it also is critical to be on the lookout for skin changes that appear in less-pigmented areas of the body, such as the palms of the hands, soles of the feet and nail beds. A skin cancer specialist should promptly examine any suspicious lesions on those sites.

How can you avoid it?

People of all ethnicities should heed the following guidelines from the Skin Cancer Foundation:

● Seek the shade, especially between 10 a.m. and 4 p.m.

● Do not burn.

● Avoid tanning and UV tanning booths.

● Cover up with clothing, including a broad-brimmed hat and UV-blocking sunglasses.

● Use a broad spectrum (UVA/UVB) sunscreen with an SPF of 15 or higher every day. For extended outdoor activity, use a water-resistant, broad spectrum sunscreen with an SPF of 30 or higher.

● Apply one ounce (two tablespoons) of sunscreen to your entire body — even on skin that clothes will cover — 30 minutes before going outside. Reapply every two hours or immediately after swimming or excessive sweating. Use sunscreen year-round and in all kinds of weather, including overcast days.

● Keep newborns out of the sun. Sunscreen should be used on babies older than 6 months.

● Examine your skin head to toe every month.

● See a physician every year for a professional skin exam.