Sunscreen labels get more attention than any other line on a skincare bottle, and most of it is confused. SPF and PA ratings do measure real things — but not the things people usually think.
SPF (Sun Protection Factor) measures protection against UVB rays specifically, the ones that cause sunburn. An SPF 30 sunscreen filters about 97% of UVB, SPF 50 about 98%. That gap looks small on paper, and it is — the bigger practical difference is almost always how much product actually gets applied, not which number is on the bottle. Most people apply a quarter to a third of the amount used in the lab tests that generate SPF numbers, which quietly cuts real-world protection well below the label claim.
PA rating, common on sunscreens sold across Asia, measures UVA protection separately — the wavelength linked to longer-term skin changes rather than sunburn. PA+ to PA++++ indicates the strength, with PA++++ offering the broadest UVA filtering. A sunscreen can carry a high SPF and a weak PA rating, or the reverse; the two numbers are not the same test and one doesn't imply the other.
A practical amount for the face alone is roughly a level teaspoon — more than most people expect, and more than fits comfortably under makeup, which is one reason reapplication gets skipped. Reapplication matters because sunscreen filters degrade with UV exposure over the day; a morning application does not carry full strength eight hours later, sweat or water resistance ratings aside.
this contact form is a decent place to start if you want product-specific advice rather than general labels, since formulations vary a lot between mineral (zinc oxide, titanium dioxide) and chemical filters (avobenzone, octinoxate) — mineral sits on top of skin and reflects, chemical absorbs and converts UV to heat, and people react differently to each depending on skin type.
Storage matters too. Sunscreen left in a hot car or on a sun-facing windowsill degrades faster than the printed expiry suggests — heat breaks down the active filters before the tube says so. Keep it somewhere closer to room temperature and check the batch code (a small printed code, separate from the expiry date) if the tube has sat around for a year or more.
None of this is about treating a skin condition. It's just what SPF and PA numbers are actually testing, so the label means something before you buy it. For general daily wear, dermatology guidance in most markets settles on SPF 30 or higher with broad-spectrum (UVA+UVB) coverage as the baseline, reapplied roughly every two hours outdoors — not a higher number bought once and forgotten.
If you're building a simple routine and want to know where a product fits before spending on it, read more about how we source and vet what we recommend, or get in touch with specific questions about your skin type.