Skin & Grooming · Explainer
Sunscreen: The Three Things That Matter and the Rest You Can Ignore
SPF above 50 is nearly a rounding error. The number that actually predicts whether sunscreen works for you is how likely you are to put it on again tomorrow.
Daily sunscreen does more for how your face ages than every serum stacked on top of it. It is also the product category where the marketing focuses hardest on the least important variable.
1. Broad spectrum, not just SPF
SPF measures protection against UVB — the wavelength that burns you. UVA penetrates deeper, does not burn, and drives a large share of photoaging. A high SPF with poor UVA coverage protects you from the sunburn and not from the wrinkles.
Look for "broad spectrum" on the label. In the US that phrase is regulated and requires the product to pass a UVA test. Without it, the SPF number is telling you about half the problem.
2. SPF 30 to 50 is the useful range
The relationship is not linear, and the top of the range is oversold:
- SPF 15 blocks about 93% of UVB
- SPF 30 blocks about 97%
- SPF 50 blocks about 98%
- SPF 100 blocks about 99%
Going from 30 to 50 buys you roughly one additional percentage point. Going from 50 to 100 buys you another one. Meanwhile the lab test that produces an SPF number uses about 2 mg of product per square centimeter of skin — considerably more than most people apply. Under-application costs you far more protection than the difference between SPF 50 and SPF 100.
The practical conclusion: pick something in the 30–50 range, and spend your attention on applying enough of it.
3. The one you will actually wear
This is the variable that decides the outcome, and no label reports it.
A sunscreen that pills under a beard, leaves a white cast, stings your eyes, or feels like cake frosting is a sunscreen you will skip on a cloudy Tuesday. Skipped days are the entire ballgame. A pleasant SPF 30 you apply daily beats an unpleasant SPF 70 you apply on beach days.
Two things help here. Chemical (organic) filters tend to be lighter and disappear on the skin, though some people find them irritating. Mineral filters — zinc oxide and titanium dioxide — are gentler on reactive skin but more likely to leave a cast, especially on deeper skin tones. Neither is safer or more effective as a class; they are different tradeoffs.
European and Asian markets have access to newer filters that are more elegant and better at UVA than most of what the US approves, which is why enthusiasts import them. If you have found a US product you like, you do not need to.
What to ignore
- "Reef safe." Unregulated as a marketing term.
- "Waterproof." Not permitted in the US; the legal term is water resistant, at 40 or 80 minutes, and both mean reapply.
- Added antioxidants. Not a reason to choose one sunscreen over another. Vitamin C and E in a sunscreen are a minor bonus at best.
- Anything above SPF 50 as a selling point.
The rule
Broad spectrum, SPF 30–50, in a texture you do not resent. Apply more than feels necessary, and reapply if you are outside for hours. That is the whole protocol.