The Ultimate Sunscreen Reapplication Cheat Sheet
Save-and-screenshot reapplication guidance for every scenario.
A full adult body needs roughly one ounce — about a shot glass — of sunscreen.
SPF 30 blocks about 97% of UVB; SPF 50 blocks about 98% — a smaller gap than the numbers suggest.
Frequently asked questions
How much sunscreen should I actually apply?
Most people apply far too little. Sunscreen is tested at 2 mg/cm², but typical use is a quarter to half that — which can drop an SPF 50 to real-world SPF 15 or lower. Aim for about a quarter to half teaspoon for the face and roughly a shot glass (1 oz) for the whole body.
How often do I need to reapply sunscreen?
Reapply about every two hours of sun exposure, and immediately after swimming, heavy sweating or toweling off. Indoors and away from windows you generally don't need to reapply, but a single morning application also wears off — so reapply if you're near windows or heading back outside.
Does a higher SPF mean more protection?
Only marginally. SPF 30 blocks about 97% of UVB, SPF 50 about 98%, and SPF 100 about 99% — and no sunscreen blocks 100%. Applying enough and reapplying matters far more than chasing a high number, and SPF says nothing about UVA protection.
r/SkincareAddiction: 'Does sunscreen completely stop you from tanning?'
Sources & citations
- EWG, 'What's Wrong With High SPF?' report
- chemistconfessions.com ↗