UV index 4: how long until skin burns?
UV index 4 falls in WHO's Moderate category. Without protection, very fair skin (type I) can start to redden in about 25 minutes, and olive skin (type IV) in about 75 minutes. These are rough estimates, not safe times.
Moderate · 3–5 Protection needed: midday shade, shirt, hat, sunglasses and sunscreen.
A warning, not a safe time. Redness shows up hours later.
Minutes to first redness by skin type
| Type IAlways burns, never tans; very pale skin, often freckles or red hair | about 25 minutes |
|---|---|
| Type IIUsually burns, tans with difficulty; fair skin, often light eyes | about 35 minutes |
| Type IIISometimes burns, tans gradually; light to light olive skin | about 50 minutes |
| Type IVRarely burns, tans easily; olive or light brown skin | about 75 minutes |
| Type VVery rarely burns, tans darkly; naturally brown skin | about 100 minutes |
| Type VIAlmost never burns; naturally dark brown to black skin | more than 2 hours |
What WHO advises at this level
From UV 3 upward, WHO says protection is needed. Seek shade during the midday hours, wear a shirt, a broad-brimmed hat and sunglasses, and apply broad-spectrum sunscreen of at least SPF 15 to skin you cannot cover. Use these measures together. Unprotected fair skin can start to redden in 20 to 45 minutes.
When and where you see this level
UV 4 is a typical clear-sky midday value in central Europe in late April and early September, and around the Mediterranean in March and October. On summer days it appears a few hours before and after midday.
What this means if you want a tan
UV 4 tans skin faster and burns it faster too: very fair skin can start to redden in about 25 minutes. A tan gives little protection, roughly SPF 4 for a dark tan according to WHO, so it is no reason to skip shade or clothing.
Frequently asked questions
How long does it take to burn at UV 4?
Rough estimates for unprotected skin at UV 4: type I: about 25 minutes; type II: about 35 minutes; type III: about 50 minutes; type IV: about 75 minutes. Redness usually appears hours later, and some people burn sooner. These are not safe times.
Is UV 4 high?
Moderate (3–5). From UV 3 upward, WHO says protection is needed. Seek shade during the midday hours, wear a shirt, a broad-brimmed hat and sunglasses, and apply broad-spectrum sunscreen of at least SPF 15 to skin you cannot cover. Use these measures together. Unprotected fair skin can start to redden in 20 to 45 minutes.
Can you tan at UV 4?
UV 4 tans skin faster and burns it faster too: very fair skin can start to redden in about 25 minutes. A tan gives little protection, roughly SPF 4 for a dark tan according to WHO, so it is no reason to skip shade or clothing.
Sources
- WHO, WMO, UNEP, ICNIRP (2002): Global Solar UV Index – A Practical Guide
- WHO (2022): Radiation – The ultraviolet (UV) index, questions and answers
- ICNIRP with ILO and WHO (2007): Protecting Workers from Ultraviolet Radiation (skin types and SED, Table 1)
- Journal of Cosmetic Dermatology: Fitzpatrick skin phototypes with typical minimal erythema dose (Table 1, after Fitzpatrick 1988 and Pathak 1987)
- CIE: Standard Erythema Dose, a Review (1 SED = 100 J/m²)