DermUV
Skin Cancer
The three most common skin cancers are basal cell carcinoma, squamous cell carcinoma, and melanoma — all linked to cumulative UV exposure.
Skin Cancer explained
1 in 5 Americans will develop skin cancer in their lifetime (AAD). UV is classified as a Group 1 carcinogen by the IARC. Daily broad-spectrum SPF 30+ has been shown in randomized trials (Green et al., 2011) to reduce melanoma risk by up to 50%.
Related terms
Terms related to Skin Cancer connect the UV and sunscreen topic cluster.
Related DermUV pages
Continue with reference material and live city UV forecasts.
Context behind Skin Cancer
Burn-time figures come from minimal erythemal dose (MED) values published for each Fitzpatrick skin type, divided by the erythemal irradiance at a given UV index. Personal MED varies by roughly 20 percent, so treat every number as a planning range.
Sunscreen labels are tested at 2 mg/cm². Typical real-world application is closer to half that, so DermUV assumes about half the labelled SPF when it estimates protected time.
Cloud cover is not protection. Thin or broken cloud can still pass most incoming UV, and light cloud edges can briefly scatter more UV toward the ground than a clear sky.
Plan outdoor blocks around the peak UV window, usually between 10am and 4pm local time. Shade, UPF fabric, a wide-brim hat, and UV-blocking sunglasses reduce dose more reliably than sunscreen alone.
Reapplication matters more than the SPF number. Reapply roughly every two hours outdoors and immediately after swimming, heavy sweating, or towelling, regardless of what the bottle claims.
UV scale reference
The WHO scale groups UV 1-2 as low, 3-5 as moderate, 6-7 as high, 8-10 as very high, and 11 or above as extreme. Protection is recommended from UV 3 upward, and shade during the middle of the day becomes the priority from UV 8 upward.
A practical routine at moderate-to-high UV is roughly one ounce of broad-spectrum sunscreen for full-body coverage, applied 15 minutes before going out, then reapplied on schedule. Clothing, hats, and shade carry the rest of the load, especially for children and anyone with a history of easy burning.
Keep exploring DermUV
These pages give more depth around skin cancer, from UV-scale reference material to definitions and city forecasts.
- Today's highest UV cities
- UV and sunscreen glossary
- UVA and UVB explained
- UVB definition
- What UV index 9 means
- What UV index 5 means
- What UV index 3 means
Numbers are modelled, not measured at your exact location, so treat them as guidance for planning rather than exact thresholds.