Sunburn Risk & SPF Calculator
Calculate how long you can stay in the sun with your sunscreen SPF before burning. Find safe exposure times for your skin type, UV index, and location.
Sun Protection Guide
How SPF Works
SPF (Sun Protection Factor) measures protection against UVB rays (burning). SPF 30: blocks 97% of UVB rays. Allows 1/30th of UVB through. SPF 50: blocks 98%. Allows 1/50th through. SPF 100: blocks 99%. Allows 1/100th through. The time calculation: unprotected burn time × SPF = protected time. Type II skin, UV Index 6: unprotected burn time ≈ 10 minutes. With SPF 30: 10 × 30 = 300 minutes theoretically. In practice: this theoretical maximum assumes perfect, generous application — most people appl
UVA vs UVB
UVB rays: cause sunburn (the 'B' = burning). Measured by SPF. More intense at midday and in summer. Blocked by glass. UVA rays: cause tanning and aging ('A' = ageing). Penetrate deeper into skin. Year-round, consistent throughout the day. NOT blocked by regular glass — you can get UVA exposure while driving. Both cause DNA damage and increase skin cancer risk. UVA makes up approximately 95% of UV reaching Earth's surface. The star rating system (UK/EU): 1-5 stars indicates UVA protection relativ
Correct Application
Most people apply only 25-50% of the required amount — this dramatically reduces actual SPF. Required amount: 2mg per cm² of skin. Face: approximately 1/4 teaspoon (1.25mL). Full body: approximately 6 teaspoons (30mL) = a shot glass. Most sunscreen bottles are used for 4-6 applications per bottle — far fewer than the label implies. Application timing: 15-30 minutes before sun exposure for chemical sunscreens (allows absorption). Mineral (physical) sunscreens (zinc oxide, titanium dioxide): work
Vitamin D and Sun Protection
Vitamin D synthesis: skin produces vitamin D when UVB hits it. In the UK: adequate vitamin D synthesis possible from March to October at midday. In winter: sun is too low to trigger significant vitamin D production. Sunscreen and vitamin D: SPF 30 applied correctly reduces vitamin D synthesis by approximately 97% (same as UVB blockage). However: very few people apply enough sunscreen to fully block synthesis. Most studies show that sunscreen use does not cause deficiency in real-world use. Suppl
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