Does sunlight cause melanoma?

Yes, sunlight is a cause, though not the only one. The National Cancer Institute states that "UV radiation from the sun, sunlamps, and tanning booths causes damage that can lead to skin cancer." Melanoma is one type of skin cancer.

Notice what that sentence includes. The sun is one source of ultraviolet radiation among several. A tanning bed delivers the same kind of damage indoors, in winter, at any latitude. NCI's advice on sun exposure is to limit time in the sun and to "avoid other sources of UV radiation, such as tanning beds."

The rest of the risk picture

UV is the biggest lever most people can pull, but NCI's melanoma summary lists several risk factors, and some have nothing to do with sun exposure at all.

Sun-related ones include "being exposed to natural sunlight or artificial sunlight (such as from tanning beds)" and "having a history of many blistering sunburns, especially as a child or teenager." That second item is worth pausing on. Damage from decades ago still counts, and burns in childhood carry particular weight.

The rest are about you rather than your habits. NCI lists "having a fair complexion, which includes: fair skin that freckles and burns easily, does not tan, or tans poorly." It lists "having several large or many small moles" and "having a family history of unusual moles." It also lists "having a family or personal history of melanoma."

This is why melanoma is not only a story about sunbathing. Someone careful with sunscreen their whole life can still develop it, and melanoma can appear on skin that rarely sees daylight.

Why this particular skin cancer gets the attention

Melanoma is not the most common skin cancer. It is the most dangerous one. NCI puts it plainly: melanoma "is much less common than the other types but much more likely to invade nearby tissue and spread to other parts of the body." And: "most deaths from skin cancer are caused by melanoma."

What protection actually looks like

NCI gives numbers rather than vague advice. The sun's rays are strongest "between 10:00 a.m. and 4:00 p.m.," so that is the window to plan around. Use sunscreen "with a sun protection factor (SPF) of at least 15," and NCI adds that "some doctors suggest using a product with an SPF of at least 30." Cover up where you can: "wear long sleeves and long pants. Tightly woven, dark fabrics are best."

The five letters to remember

Early melanoma is highly treatable, and finding it early is mostly a matter of noticing. NCI teaches the ABCDE rule for moles.

• A is for asymmetrical. If you divide the mole in half, "the 2 halves are different in size or shape."
• B is for border. The edges are irregular rather than clean.
• C is for color. More than one color is present in the same mole.
• D is for diameter. "Melanoma is usually larger than 6 millimeters," roughly the width of a pencil eraser.
• E is for evolving. "The mole changes in size, shape, or color over time."

E is the most useful letter, because change beats any single snapshot. NCI also flags moles that itch, ooze, bleed, or become ulcerated, plus new moles growing beside an existing one.

Check your own skin, and ask someone to check your back and scalp. If any of these show up, NCI's instruction is short: check with your doctor.