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The ABCDE criteria

These are the American Academy of Dermatology’s definitions, quoted as the AAD words them.

Note what D actually says. The six-millimeter figure describes melanomas at the point they are usually caught, not a threshold below which a spot is safe. Plenty are found smaller. Treat it as a prompt to look closely rather than a rule for dismissing something.

The ugly duckling sign

Most people’s moles look broadly like each other. The ugly duckling rule uses that: “If any mole stands out or looks different from that of surrounding moles, it is the ugly duckling, the odd-mole-out, the ‘lone ranger’.”

This works precisely where ABCDE struggles: on someone with dozens of moles, where evaluating each one against a checklist is impractical and half of them will trip at least one criterion. Scanning for the one that does not match its neighbors is faster and, for many people, more reliable. It also catches melanomas that are individually unremarkable but obviously different from that person’s pattern.

EFG: the ones ABCDE misses

Nodular melanoma is the subtype most likely to slip past the ABCDE checklist, because it is often symmetrical, evenly colored, and regular-bordered. It is also fast-growing. The additional signs are:

• Elevated. Raised above the surrounding skin rather than flat.
• Firm. Solid to the touch.
• Growing. Changing over weeks, not years.

A raised, firm lump that has appeared or changed over the past few weeks deserves attention even if it looks unremarkable by ABCDE.

If you have darker skin, look in different places

Melanoma is far less common in people with darker skin. The American Cancer Society puts lifetime risk at roughly 1 in 33 for white people, about 1 in 200 for Hispanic people, and about 1 in 1,000 for Black people. But when it does occur it is much more often advanced by the time it is found, and part of the reason is location.

The AAD notes that in darker skin tones, skin cancer “may show up in areas that receive little, if any, sun”: the palms, the soles of the feet, between and under the toes, the fingernails and toenails, inside the mouth, and the buttocks and genital area. As the AAD puts it, “many people never think about checking their feet for signs of skin cancer, so the cancer often spreads before it’s noticed.”

So the additional things to check are:

• The soles of both feet, and the skin between every toe.
• The palms of both hands.
• Fingernails and toenails, specifically for a dark line or streak running the length of the nail, or pigment spreading onto the surrounding skin.
• Any sore that does not heal.
• Darkening on the lips, inside the mouth, on the scalp, or in the genital area.

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How to check your own skin properly →
What happens at a professional skin exam →