UV Index explained

The UV Index (UVI) is a scale developed by the World Health Organization to communicate the intensity of ultraviolet radiation reaching the Earth’s surface. It measures weighted irradiance in the 290–400 nm wavelength range:

UV Index	Exposure level	Recommended action
1–2	Low	No protection needed for most people
3–5	Moderate	Sunscreen SPF 30+, seek shade near midday
6–7	High	SPF 30+ required, protective clothing recommended
8–10	Very high	SPF 50+, minimize time in direct sun
11+	Extreme	SPF 50+, avoid outdoor exposure near midday

SPF and UPF guidance

SPF (Sun Protection Factor) measures protection against UVB rays only (the rays that cause sunburn). SPF 30 blocks about 97% of UVB; SPF 50 blocks about 98%. Broad- spectrum sunscreens also cover UVA rays (which cause aging and contribute to skin cancer) - always choose broad-spectrum. Reapply every 2 hours and after swimming or sweating.

UPF (Ultraviolet Protection Factor) applies to clothing and fabric. A UPF 50 garment blocks 98% of UV radiation. Standard cotton T-shirts typically have a UPF of only 5–15.

Skin type and burn time

The Fitzpatrick scale classifies skin phototypes I–VI. Approximate unprotected burn time at UV Index 6:

Fitzpatrick type	Description	Approx. burn time (UVI 6)
Type I	Very fair, always burns	~10 min
Type II	Fair, usually burns	~15 min
Type III	Medium, sometimes burns	~20 min
Type IV	Olive, rarely burns	~30 min
Type V	Brown, very rarely burns	~45 min
Type VI	Dark brown/black, almost never burns	~60+ min