Five minutes, then stop
SPF 30 vs SPF 50
SPF 30 blocks about 97% of tested UVB in the lab. SPF 50 about 98%. The jump is small on paper and large in real life because nobody applies the lab amount.
Updated 27 Aug 2026 · 6 min read · SPF 30 vs SPF 50
The lab number is a ratio
SPF is mostly a UVB/sunburn number. UVA protection depends on the filter mix (PA+, PPD, ‘broad spectrum’). A 30 that is actually broad spectrum and on thickly beats a 50 that is a mist you forgot. The 97% versus 98% line is true in the test. In a bathroom at 7:40am, 50 is a hedge.
For a desk day with a window, 30 done well is fine. For a six-hour terrace, 50, hat, reapply.
Why 50 wins as a household default
Most faces get a third to half of the tested dose. If you think you applied 50 and you applied a 50 at half thickness, you are living in the 20s. Starting at 50 leaves more room for that. Makeup with SPF 15 is not a sunscreen.
- Daily city: 30 or 50, two fingers, every morning
- High UV / snow / water: 50, reapply, cover
- SPF in foundation: a bonus, not the dose
Numbers that are noise
SPF 70 versus 50 in a drugstore aisle is a rounding fight. Texture you will use is the product. A 30 you reapply at lunch beats a 50 you hate and skip. Check the date before you trust last year’s 50.
Questions, answered
- Can I mix SPF 30 and 50?
- You can layer. You cannot average them into 40 in any way that should comfort you. Apply a full dose of one.
- Is SPF 15 moisturizer enough?
- As the only sun product on a July face, no. As extra under a real sunscreen, whatever.
- Does a higher SPF last longer?
- No. Time in the sun, sweat, and towel still win. Reapply.
