You buy SPF 50. You put a little on in the morning. You feel safe all day. It's one of the most widespread mistakes in skincare, and expert Rachel Kiss says every season she sees the same pattern: people who think they're fully protected, while the skin is actually getting much less defense than what it says on the packaging.

"One of the most common mistakes is to think that high SPF, like SPF 50, holds its efficiency all day on its own," Kiss says. "The problem usually isn't with the product, but with how it gets applied and reapplied." SPF is a film - when it isn't applied evenly, vulnerable zones open up. The gap between theoretical and real protection can be huge.

The second problem: reapplication. Most people put SPF on skin that already has sebum, sweat, pollution, and the previous product. "Many people believe that touching up SPF without cleaning the skin first is enough, but it actually reduces effectiveness." The recommendation: reapply every two hours when you're in the sun, and immediately after swimming or heavy sweating.

Another technical detail: the two-finger rule for the face. Cover both the index and middle finger along their full length - that's the amount of SPF that should go on your face. Less and you won't get the protection on the bottle. If you're wearing makeup during the day, use a spray, stick or SPF powder to top up - it doesn't weigh down the face and doesn't move the previously applied layers.

The sun isn't the enemy - it's part of life. But SPF 50 is not a magic shield. It's an instrument that, like every tool, requires proper use. Everything else is pseudo-protection - a feeling of safety without reality behind it.