Every two hours, everywhere, forever? PA ratings? Tinted formulas? What the reapplication rules and the ratings actually mean, and which habits earn their effort.
Sunscreen advice gets repeated with the confidence of law and the precision of folklore. Since it's the single most evidence-backed step in skincare, it deserves better — here's the folklore, checked.
"Reapply every two hours" — real rule, wrong scope. The two-hour guidance exists because sunscreen rubs off, sweats off, and degrades during sun exposure — the AAD's actual framing is every two hours outdoors, and after swimming, sweating, or toweling [1]. It was never a decree to scrub and reapply at your desk. Indoors away from direct sun, a generous morning application is doing its job for the day; sitting in a literal sunbeam by a window, a midday top-up is reasonable. The habit with trial evidence behind it is daily use: in the randomized Nambour trial, adults assigned to daily sunscreen showed measurably less skin aging over 4.5 years than the use-it-when-you-like group — 24% less [2]. Consistency, not heroic reapplication frequency, was the variable that mattered.
"SPF 50 is barely better than SPF 30" — misleading arithmetic. The percentages (SPF 30 blocks ~97% of UVB, SPF 50 ~98%) hide the useful number: transmitted UV. SPF 30 lets through roughly 1 in 30 burning photons, SPF 50 roughly 1 in 50 — about 40% less UV reaching your skin. More importantly, everyone applies less than the tested amount, which drops real-world protection well below the label; a higher SPF buys margin for that universal under-application. Speaking of which: the tested dose corresponds to about a quarter teaspoon for the face. Most people use a fraction of it. Applying enough is worth more than any other upgrade in this article [1].
"PA++++ is marketing tiers." PA is a real measurement — the Asian-market grading of UVA protection, based on a lab endpoint called persistent pigment darkening (PPD). SPF grades UVB, the burning wavelengths; PA grades UVA, the deeper-penetrating wavelengths that drive photoaging and pigment without announcing themselves. More plus marks = higher measured UVA tier. If aging or dark spots are your concern, the PA rating (or "broad spectrum" in the US system) is not optional fine print.
"Tinted sunscreen is just makeup." The tint is iron oxides, and they do something UV filters don't: block visible light. For most people that's irrelevant — visible light doesn't burn. But for melasma and stubborn pigmentation, especially in deeper skin tones, visible light measurably drives pigment, and tinted mineral sunscreens have controlled-trial support for protecting against it where UV-only filters miss [3]. If you're treating dark spots, the tint is functional.