Sunburn is not a souvenir — it is a radiation burn that doubles melanoma risk with five lifetime events. The sunscreen aisle is a minefield of marketing terms (reef-safe, sport, baby, mineral, chemical, SPF 100). Here is the evidence-based guide: what to buy, how to apply, and the three mistakes that waste the bottle.
The only three specs that matter
- Broad spectrum (UVA + UVB): non-negotiable. UVA ages (wrinkles, spots); UVB burns. Both cause cancer.
li>SPF 30–50: SPF 30 blocks 97% UVB; SPF 50 blocks 98%. SPF 100 blocks 99% — not double protection, double chemicals. Diminishing returns above 50.
li>Water resistance 80 minutes: the maximum FDA rating. “Waterproof” and “sweatproof” are banned terms; do not trust them.
Mineral vs chemical — the honest take
- Mineral (zinc oxide, titanium dioxide): sits on skin, reflects UV, immediate protection, reef-safe, less irritation. White cast on darker skin (tinted versions exist). Best for: face, kids, sensitive skin, reef areas.
li>Chemical (avobenzone, octocrylene, homosalate, etc.): absorbs UV, converts to heat, 15 min to activate, cosmetically elegant, some harm coral (oxybenzone, octinoxate banned in Hawaii/Key West/Palau). Best for: body, daily wear, darker skin tones.
li>Hybrid: mineral + chemical — best of both, common in modern “reef-safe” formulations.
The application protocol (most people do it wrong)
- li>Amount: 2 mg/cm² = 30 ml (shot glass) for full adult body. Most apply 0.5–1 mg/cm² = 25–50% labelled SPF.
li>Timing: chemical = 15 min before sun; mineral = immediate.
li>Reapply: every 80 minutes in water/sweat; every 2 hours dry. Towel dry = reapply immediately.
li>Face: 1/4 tsp (nickel-sized dollop). Ears, neck, scalp (part line), tops of feet.
The three mistakes that waste the bottle
- li>Spray and walk away: aerosol sprays deposit 30–50% on air/wind. Spray into hand, then apply. Or use lotion.
li>Expired product: chemical filters degrade 12–18 months; mineral stable 3 years. Check the PAO (open jar symbol).
li>Relying on makeup SPF: foundation SPF 15 applied at makeup thickness = SPF 3–4. Not a substitute.
The reef-safe reality
“Reef-safe” is unregulated. Look for: **no oxybenzone, no octinoxate, no octocrylene, non-nano zinc oxide/titanium dioxide**. Brands that consistently pass: Thinksport, Badger, Blue Lizard, Stream2Sea, All Good. Price: 12–20 euro/100 ml.
One-line verdict
Broad spectrum SPF 30–50, water resistant 80 min, mineral for face/kids/reef, chemical for body, 30 ml per application, reapply every 80 min — the protocol that actually protects.