The short answer
Sunscreen helps protect skin from ultraviolet rays that can cause skin cancer. Choose a broad-spectrum product with SPF 30 or higher, apply plenty of it, and reapply every couple of hours. Sunscreen is one useful layer of protection, not a substitute for shade and clothing.
Look for broad-spectrum sunscreen with SPF 30 or higher.
Most people apply too little; use a generous amount on all exposed skin.
Reapply at least every 2 hours, and after swimming, sweating, or toweling off.
Sunscreen has limits — it should be used with shade and clothing, not instead of them.
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The full explanation.
The simple version
Sunscreen helps shield your skin from ultraviolet (UV) rays, the invisible energy from the sun that can lead to skin cancer. Used well, it is a simple and useful part of protecting your skin.
But sunscreen only works if you pick a good one, put on enough, and reapply. And it works best when it is one layer among several — not the only thing standing between you and the sun.
Choose broad-spectrum, SPF 30 or higher, apply plenty, and reapply often.
Reading the label
Two words on the label matter most:
- Broad-spectrum. This means the product protects against both UVA and UVB rays. Both types damage skin, so you want protection from both.
- SPF 30 or higher. SPF, or Sun Protection Factor, measures protection against the UVB rays that cause sunburn. SPF 30 blocks about 97 percent of UVB. Higher numbers add just a little more, and none reach 100 percent.
If you will be swimming or sweating, look for a water resistant label. Note that this only lasts for a set time in the water — usually 40 or 80 minutes — not forever.
Broad-spectrum plus SPF 30 or higher is the everyday standard.
How much to apply
This is where most people fall short. Using too little sunscreen gives you far less protection than the SPF promises.
- For an adult, about one ounce — roughly a shot glass full — covers the exposed body.
- Use about a nickel-sized amount for the face alone.
- Apply about 15 minutes before going outside so it can bind to the skin.
Do not miss easy-to-forget spots: ears, the back of the neck, the hairline, the tops of feet, and hands. Use an SPF lip balm for your lips.
A thin layer is a weak layer — be generous.
Reapplying
Sunscreen wears off, so one application is not enough for a day outdoors.
- Reapply at least every 2 hours.
- Reapply after swimming, heavy sweating, or toweling off, even with a water-resistant product.
Setting a phone reminder or keeping sunscreen in your bag makes this easier to remember.
The limits of sunscreen
Sunscreen is helpful, but it has real limits worth knowing:
- No sunscreen blocks all UV. Some rays still get through.
- People often use it to stay out longer. If sunscreen lets you skip a sunburn but you spend all day in the sun, you may still get a large dose of UV.
- It can be applied unevenly, leaving gaps.
Because of this, experts stress that sunscreen should be used together with shade, clothing, a hat, and sunglasses — not as a reason to skip them.
Sunscreen is a teammate to shade and clothing, not a replacement.
Storage and expiration
Sunscreen loses strength over time and in high heat. To keep it working:
- Check the expiration date. Sunscreens are made to last at least 3 years, but many print a date.
- Replace bottles that are expired or that have been left in a hot car for long periods.
- Toss any product that has changed color, texture, or smell.
Chemical or mineral — does it matter?
You may see sunscreens described as mineral (with ingredients like zinc oxide or titanium dioxide) or chemical (with ingredients that absorb UV). Both types can protect your skin when they are broad-spectrum and SPF 30 or higher.
- Mineral sunscreens sit on top of the skin and start working right away. They can feel thicker or leave a slight white cast. Many people find them gentle on sensitive skin.
- Chemical sunscreens tend to be lighter and rub in more clearly, which some people prefer for daily use.
The best sunscreen is the one you will actually use, apply well, and reapply. If one type irritates your skin or you simply dislike how it feels, trying the other is reasonable.
Whichever type you choose, applying enough and reapplying matters far more than the category on the label.
A quick word on children
Sunscreen can be used on children, and it is an important layer for kids old enough for it. For babies under 6 months, shade and clothing are usually preferred, since their skin is especially delicate. Ask your child's care team about the right approach for your baby.
Making sunscreen part of a daily routine — kept by the door, in a bag, or in the car — helps the whole family remember it. Small, steady habits add up to real protection over the years.
Words to know
Tap any term to see what it means.
Common questions
▸What does broad-spectrum mean?
Broad-spectrum means the sunscreen protects against both UVA and UVB rays. UVB causes sunburn and UVA adds to deeper skin damage. Both contribute to skin cancer, so broad-spectrum protection covers both.
▸What SPF should I choose?
Experts generally recommend an SPF of 30 or higher for everyday use. SPF 30 blocks about 97 percent of UVB rays. Higher SPF numbers add only a little more protection, and no sunscreen blocks everything.
▸How much sunscreen should I use?
Most people use far too little. A common guide for an adult is about one ounce — roughly a shot glass full — to cover the exposed body, and about a nickel-sized amount for the face. Applying too little sunscreen gives you less protection than the SPF number promises.
▸How often do I need to reapply?
Reapply at least every 2 hours. Reapply sooner after swimming, sweating heavily, or toweling off, even if the label says water resistant. Water-resistant labels only last for a stated time in the water, usually 40 or 80 minutes.
▸Does sunscreen expire?
Yes. Sunscreen is required to stay effective for at least 3 years, and many have an expiration date printed on them. If yours has expired or has been exposed to high heat, replace it, since it may no longer protect you well.
▸Is spray sunscreen as good as lotion?
Sprays can work but are easy to apply too thinly or miss spots, and they can blow away in wind. If you use a spray, apply until the skin glistens and rub it in, and never spray it directly on the face — spray your hands first, then apply.
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