Application & Usage Myths
The Sunscreen Step People Skip: Letting It Dry
Rushing the dry-down ruins your coverage.
SPF 15 blocks ~93% of UVB, SPF 30 ~97%, SPF 50 ~98%, SPF 100 ~99%.
Apply too little and an SPF 50 can perform more like an SPF 15 in real life.
Questions we get a lot
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.
r/SkincareScience: 'Is SPF 100 a marketing gimmick or worth it?'