The short answer
Ultraviolet (UV) radiation damages skin cell DNA. Daily sun protection and skin self-exams are the primary defenses against melanoma and non-melanoma skin cancers.
Ultraviolet radiation damages the DNA inside skin cells, and that damage drives skin cancer risk.
The ABCDE rule for self-exams: asymmetry, border irregularity, color variation, diameter over 6 mm, and evolving.
Daily sun protection and regular self-exams are the main defenses against melanoma and non-melanoma skin cancers.
NCI advises sunscreen with an SPF of at least 15, applied 30 minutes before going out and again every two hours.
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Why the sun matters for your skin
This page is for anyone who wants to lower their risk of skin cancer. It covers how to limit sun exposure, how to check your own skin, and when to call your care team.
Ultraviolet (UV) rays are an invisible part of sunlight. They damage the DNA inside skin cells. Daily sun protection and skin self-exams are the main defenses against melanoma and other skin cancers.
How to lower your exposure
NCI advises people of all ages and all skin tones to limit time in the sun, especially from mid-morning through late afternoon, and to avoid tanning beds. Its practical tips:
- Cover up. Wear a hat with a wide brim all the way around, so it shades your face, neck and ears. A baseball cap or visor only shades part of you. Long sleeves and long pants help, and tightly woven dark fabrics work best. Some clothing carries a UPF rating; a higher number means more protection.
- Protect your eyes. Wear sunglasses that block UV radiation. They also shield the skin around your eyes.
- Use sunscreen properly. NCI advises an SPF of at least 15. Put it on 30 minutes before you go out. Apply it again every two hours, and after swimming or sweating. Ask your care team whether a higher SPF suits you.
Two things surprise people. UV rays are strongest between 10 a.m. and 4 p.m., and they pass through light clothing, windows, windshields and clouds. Sand, water, snow, ice and pavement all reflect them back at you.
Skin cancer is more common in people with lighter skin. But NCI is clear that people of every skin tone can develop it, including people with dark skin.
Checking your own skin
NCI advises telling your doctor if you notice a mole that changes. The changes worth reporting are:
- The color changes.
- It gets bigger or smaller, or changes shape, texture or height.
- The skin on the surface becomes dry or scaly.
- It becomes hard, or feels lumpy.
- It starts to itch.
- It bleeds or oozes.
People with many moles, or with several large ones, have a higher risk of melanoma. NCI says people with dysplastic nevi, which are unusual-looking moles, should check their skin each month and have regular exams by a doctor.
Frequently Asked Questions
Short answers to common questions about skin checks.
What should I look for during a skin self-exam?
Use the ABCDE rule. It stands for Asymmetry, Border irregularity, Color that varies, Diameter over 6 mm, and Evolving. Evolving means the spot changes in size, shape, or color.
Questions to Ask Your Care Team
- "Which sunscreen and SPF are right for me?"
- "How often should I have a professional dermatologist skin check?"
When to get help sooner
- Call your care team the same day if a spot on your skin is bleeding, oozing, or has broken open and will not heal.
- Call your care team within a day or two if a mole changes color, shape, size, texture or height; becomes hard or lumpy; turns dry or scaly on the surface; or starts to itch.
- Call your care team within a day or two if a new spot appears that does not look like your other moles, or an old spot suddenly looks different.
Have any change checked rather than waiting to see what happens.
Sources
Common questions
What should I look for during a skin self-exam?
Use the ABCDE rule: Asymmetry, Border irregularity, Color variation, Diameter >6mm, and Evolving (changing in size, shape, or color).
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Written by: Cancer ExplainedSources last checked: 2026-10-02 what this meansLast updated: 2026-10-02Next planned review: 2027-07-23
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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