Sunscreen
How often should you reapply sunscreen?
Reapply at least every two hours while you’re in the sun — and immediately after swimming, heavy sweating or towel-drying, whatever the bottle says. “Water-resistant” formulas are typically tested for just 40–80 minutes in water, and towelling removes most of what’s left.
Why every two hours?
Sunscreen filters degrade in UV light, rub off on clothes and skin contact, and migrate with sweat and skin oils. Studies consistently show real-world protection falling well below the labelled SPF within a couple of hours. The two-hour rule isn’t marketing — it’s the point at which a typical application has thinned enough to matter.
The part everyone gets wrong: quantity
Lab SPF is measured at 2 mg of product per cm² of skin. For an adult body that’s roughly six to eight teaspoons — about a shot glass — and around half a teaspoon for face, ears and neck. Most people apply a quarter to a half of that, which cuts an SPF 30 to an effective SPF of roughly 5–10. Applying generously matters more than the number on the tube.
Reapply sooner when…
- You’ve been swimming — even “very water resistant” products are only tested to 80 minutes.
- You’ve been sweating heavily — sport, hot days, hiking.
- You’ve towelled off — towelling removes most product in one pass.
- It’s peak UV (11am–3pm) and you’re staying out — err on the side of a fresh layer.
How Soleil helps
Reminders that survive real life
Log a sunscreen application in Soleil and it schedules the next reminder — never more than two hours out, and sooner if you record swimming, sweating or towel-drying. On a family outing, each person gets their own reapply reminder, because a toddler’s schedule isn’t yours.
Crucially, Soleil never treats a reapplication as extra permitted time outside: the session clock keeps running, and protection checks stay honest.
Related questions
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Does SPF 50 last longer than SPF 30?
No. SPF describes how much UVB is filtered while the layer is intact, not how long it lasts. Both need reapplying at least every two hours, and both come off in water and on towels.
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How do I reapply over makeup?
SPF powders, sprays and cushion compacts make top-ups practical, though they rarely reach a full protective dose. On high-UV days, shade and a hat carry more of the load for your face.
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Are “once-a-day” sunscreens real?
UK consumer testing has repeatedly found protection from “once-a-day” products falls substantially over a day. Dermatology bodies and Cancer Research UK still advise reapplying every two hours regardless of the label.
Soleil is wellness guidance, not medical advice. For sensitive skin or diagnosed conditions, please follow a dermatologist’s plan.