How often should I reapply sunscreen?

Every two hours, and right after swimming, sweating, or toweling off. No sunscreen lasts a full day on one application.

Sunscreen and SPF: A Simple, Practical Guide

Q: What SPF should I use?

SPF 30 is a good everyday minimum and blocks about 97% of UVB. On high or very high UV days, or for long time outdoors, step up to SPF 50. Going far above SPF 50 adds very little.

SPF 30 is a solid everyday minimum. Use enough, reapply every two hours, and step up to SPF 50 when the UV index is high. That covers most of what you need to know.

What SPF actually means

SPF, or sun protection factor, measures how well a sunscreen blocks UVB, the burning rays. The numbers are less dramatic than they sound:

SPF 15 blocks about 93% of UVB.
SPF 30 blocks about 97%.
SPF 50 blocks about 98%.

So SPF 30 is not twice the protection of SPF 15, and SPF 100 is not twice SPF 50. After SPF 30, the gains get small. What matters far more is using enough and reapplying.

Which SPF for which UV level

0-2

Low

Usually fine without sunscreen for short spells. SPF 15+ if you burn easily.

3-5

Moderate

SPF 30 on exposed skin. This is the level where sunscreen becomes a daily habit.

6-7

High

SPF 30 to 50, reapplied every two hours. Add a hat and shade.

8-10

Very High

SPF 50, plus clothing, hat, and shade at midday.

11+

Extreme

SPF 50, full cover, and avoid the midday sun where you can.

The part people get wrong: how much

Most sunburn under sunscreen comes from using too little. To hit the SPF on the bottle, an adult needs about one ounce, a full shot glass, to cover the whole body. For the face and neck alone, think two finger lengths of product. If you apply a thin layer, an SPF 30 can perform more like an SPF 10.

Reapply, reapply, reapply

No sunscreen lasts all day. Reapply every two hours, and always after swimming, sweating, or toweling off, even the water-resistant kinds. Water resistant means it holds up for 40 or 80 minutes in water, not that it is waterproof.

Broad spectrum and a few extras

Look for broad spectrum. SPF only rates UVB. Broad spectrum means it also guards against UVA, which drives skin aging.
Mineral or chemical both work. Zinc oxide and titanium dioxide sit on top of skin; chemical filters absorb UV. Pick what feels good so you actually wear it.
Do not forget the spots. Ears, back of the neck, tops of feet, and your part line all burn.
Sunscreen is a layer, not a shield. Pair it with shade, clothing, and timing on high-UV days.

Not sure how much protection today calls for? Check the live UV index for your city and match it to the table above.

Frequently asked questions

What SPF should I use?

SPF 30 for everyday, SPF 50 on high-UV days or long time outdoors. Above 50 adds very little.

How often should I reapply?

Every two hours, and right after swimming, sweating, or toweling off.

Is a higher SPF always better?

Not really. The jump from 30 to 50 is small, and very high numbers can give false confidence. Enough product and reapplication matter more.