Why reapply sunscreen every 2 hours?

What happens to the first layer?

Sunscreen forms a protective layer on your skin that absorbs the sun's ultraviolet radiation, or UV rays. Water can wash sunscreen off, sweat can dilute it, and a towel can remove it. A fresh application restores coverage across exposed skin. Treat two hours as a reapplication interval, not a promise that the original layer will stay intact until then. Reapply the same way you applied the first coat, rather than touching up only the areas that seem most exposed.12

Does SPF 50 last longer than SPF 30?

No. A higher SPF gives greater protection against UVB, the rays chiefly responsible for sunburn, but does not extend the reapplication interval. SPF measures protection against an amount of UV exposure, not a number of hours. The same time outdoors can mean different exposure depending on the time of day and location. Choose broad spectrum SPF 30 or higher to protect against both UVA and UVB, and keep the same reapplication schedule even with SPF 50 or SPF 100.234

What if the sunscreen is water resistant?

Water resistant does not mean waterproof. Labels specify either 40 or 80 minutes of protection while swimming or sweating. Read that limit before getting in the water; neither claim means two hours of swimming protection. Reapply after swimming or sweating, following the bottle's directions, and after toweling dry. Even a water resistant sunscreen eventually washes off.135

How to apply and reapply sunscreen

1. 1Apply sunscreen to dry skin about 15 minutes before going outdoors.
2. 2Use enough for full coverage. Most adults need about one ounce to cover exposed body skin, with more needed for a larger body. For the face, use at least one teaspoon.
3. 3Rub sunscreen thoroughly into all skin not covered by clothing. Include the ears, neck, tops of the feet, hairline and exposed scalp. Use SPF 30 or higher lip balm for the lips.
4. 4Reapply every two hours while outdoors, and sooner after swimming, sweating or toweling. Cover every exposed area again.

Follow the directions for your chosen format. Never spray sunscreen directly onto your face.3

Do clouds or windows change the answer?

Cloudy weather does not remove the need to reapply outdoors, and winter sunlight still exposes skin to UV rays. Indoors, windows matter: UVA can pass through glass, while UVB is blocked. Keep exposed skin protected if you spend time in sunlight through a window. The two hour outdoor schedule is a clear rule for continued sun exposure, rather than a reason to judge protection by how warm or bright the day feels.246

How do you reapply over makeup?

Powder SPF is an option for touch ups over makeup, which gives the cosmetic brush a job beyond rearranging beige. Use powder for touch ups, not as a replacement for traditional sunscreen. SPF in foundation or moisturizer still needs reapplication when you are outdoors.127

Do not wait for redness

Redness or a prickly or burning sensation means you should act rather than wait for the next scheduled application. Move into shade and protect exposed skin. No sunscreen blocks all UV radiation, so combine sunscreen with clothing, a wide brimmed hat and sunglasses. If you take medication, ask about specific sun precautions because some medicines increase sun sensitivity.15