Sunburn Index: Understanding UV Radiation Risk

The UV Index (often called sunburn index) is a standardized scale (0–11+) measuring the intensity of sunburn-causing ultraviolet radiation at Earth's surface. Developed by WHO, WMO, UNEP, and ICNIRP.

UV Index Scale and Risk Levels

UV Index	Risk Level	Protection Needed	Time to Burn (Fair Skin)
0–2	Low	Minimal (sunglasses if bright)	>60 min
3–5	Moderate	Shade midday, hat, SPF 30+	30–45 min
6–7	High	Reduce midday exposure, full protection	15–25 min
8–10	Very High	Minimize midday sun, seek shade, SPF 50+	10–15 min
11+	Extreme	Avoid midday sun, full protection essential	<10 min

Factors Affecting UV Index

• Sun elevation (time of day, season, latitude)
• Cloud cover (thick clouds reduce; thin clouds scatter)
• Altitude (+10–12% per 1000m)
• Ozone layer thickness
• Ground reflection (snow +80%, sand +15%, water +10%)

Practical Use

• Check daily forecast (weather apps, EPA SunWise, WHO UV app).
• Apply broad-spectrum SPF 30+ 15 min before exposure; reapply 2-hourly.
• Wear UPF clothing, wide-brim hat, UV-blocking sunglasses.
• Seek shade 10 AM–4 PM (peak UV).
• Protect children – sunburns in youth double melanoma risk.

The UV Index is a vital public health tool for preventing skin cancer and photoaging.