DermUV

UVA

UVA is long-wavelength ultraviolet radiation (320–400 nm) that penetrates deeply into the dermis, drives photoaging, and contributes to melanoma.

UVA explained

UVA passes through window glass and clouds, and is present at near-constant intensity throughout daylight hours — unlike UVB, which peaks midday. PA+++ and 'broad-spectrum' labels indicate UVA protection. The critical wavelength must be ≥ 370 nm for FDA broad-spectrum status.

Related terms

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

Related DermUV pages

Continue with reference material and live city UV forecasts.

Context behind UVA

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

DermUV forecast values come from Open-Meteo UV data (CC BY 4.0) and are refreshed throughout the day.