DermUV

UVB

UVB is medium-wavelength ultraviolet radiation (280–320 nm) that drives sunburn, vitamin D synthesis, and most non-melanoma skin cancers.

UVB explained

UVB intensity peaks between 10am and 4pm and is largely blocked by window glass. SPF numbers measure UVB protection. It is also the wavelength responsible for triggering the skin's vitamin D synthesis pathway in the epidermis.

Related terms

Terms related to UVB connect the UV and sunscreen topic cluster.

Related DermUV pages

Continue with reference material and live city UV forecasts.

What to do with this UVB data

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.

The UV index is a measure of erythemal (skin-reddening) irradiance, where each whole point equals 25 mW/m² of UV energy reaching the surface. That is why burn-time estimates fall roughly by half when the index doubles.

Cumulative dose drives photoaging and long-term skin damage more than any single day. Small daily exposures on commutes, walks, and driving add up across a season.

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.

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.

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 uvb, from UV-scale reference material to definitions and city forecasts.

Numbers are modelled, not measured at your exact location, so treat them as guidance for planning rather than exact thresholds.