Maximizing Sunscreen SPF Protection

Sunscreen and Sun Safety

A mother applying sunscreen on her son.
It's best to apply sunscreen before you head out into the sun. Paul Bradbury/Getty Images

Most parents think of SPF, or Sun Protection Factor, as a way to tell how strong a sunscreen is. And while that is somewhat true, as an SPF 30 sunscreen provides more sun protection than an SPF 15 sunscreen, there is more to it than that.

For one thing, SPF is only a measure of a sunscreen's effectiveness against UVB rays. So your child might have poor sun protection, even if you're are using a high SPF 100+ sunscreen unless it also lists sunscreen ingredients that blocks UVA rays.

These sunscreens that protect against UVA and UVB rays are usually labeled as broad-spectrum sunscreens.

SPF

Another misconception about SPF is that it simply tells you how long you can stay in the sun without getting a sunburn.

While that is true, how much a sunscreen protects you -- no matter the SPF -- also depends on the intensity of the sun at the time. For example, it might take 30 minutes for a child without sunscreen to get a sunburn in the morning, but only 15 minutes in the early afternoon, when the intensity of the sun's rays are higher. And even at the same time of day, it will take less time to get a sunburn on days when the UV index is at a moderate to high level, versus days when it is low.

So while an SPF 15 sunscreen will theoretically allow your child to stay in the sun 15 times longer without getting a sunburn than he would with without sun protection, depending on the time of day and the UV Index, that may mean 4 hours or 8 hours of sun protection.

Would an SPF 50 sunscreen allow your child to stay in the sun 50 times longer, providing all day protection?

Unfortunately, no. Today's sunscreens don't offer all-day sun protection or protection that can even last more than a few hours. Too many factors can affect how well sunscreen works, including that:

  • even very water-resistant, waterproof, and sweat-proof sunscreens will begin to wash off after about 80 minutes or sooner if your child is swimming or sweating heavily
  • some sunscreen ingredients eventually begin to breakdown when exposed to the sun
  • sunscreen may actually get rubbed off while your child is playing

And many parents only use about one-fourth to half the recommended amount of sunscreen and don't reapply it often enough.

More About SPF

In general, a sunscreen with:

  • SPF 2 blocks 50% of UVB rays
  • SPF 4 blocks 75% of UVB rays
  • SPF 8 blocks 87% of UVB rays
  • SPF 15 blocks 93% of UVB rays
  • SPF 30 blocks 97% of UVB rays
  • SPF 50 blocks 98% of UVB rays
  • SPF 100 blocks 99% of UVB rays

Many experts question whether using a sunscreen above SPF 30 is really necessary,​ though, since you are already blocking 97% of UVB rays. Using a high SPF sunscreen might be a good idea and could provide more protection for those parents who don't use enough sunscreen and don't reapply it often enough.

For example, an SPF 30 sunscreen will effectively become an SPF 5 sunscreen if you only apply half the recommend amount, as many parents do.

If a high SPF 100 sunscreen decreases by the same amount, then hopefully you are still in the SPF 15 to SPF 30 range of SPF protection.

Maximizing Sunscreen SPF Protection

To get the best sun protection for their kids, in addition to reducing or limiting their sun exposure when UV rays are strongest (usually from about 10 a.m. to 4 p.m.), parents should choose a broad-spectrum sunscreen with a minimum SPF of 15 to 30 and should work to maximize the SPF protection of that sunscreen by:

  • applying sunscreen at least 15 to 30 minutes before kids will be exposed to the sun, not simply waiting until they are already outside
  • applying enough sunscreen, which may equal up to an ounce at a time for a young adult
  • applying a very water-resistant sunscreen at least 15 to 30 minutes before a child is going swimming or will be exposed to water, so there is less of chance it will be easily washed off
  • applying sunscreen evenly to all exposed body parts, especially those areas that are often overlooked, including a child's nose, the top of his feet, and the back of his neck
  • reapplying sunscreen at least every 2 hours, and especially after a child swims or plays vigorously and sweats
  • making sure sunscreen has not expired, keeping in mind that sunscreen without an expiration date is thought to lose its effectiveness after about a year or sooner if it is exposed to high temperatures, like the glove box of a car
  • not using both a sunscreen and insect repellent at the same time, or a product that combines a sunscreen and insect repellent, as DEET (a common bug spray ingredient) can lower the SPF of a sunscreen
  • using a high SPF sunscreen if you also need to use an insect repellent, but apply your sunscreen first and be sure to reapply the sunscreen every few hours

If your child is still getting tanned or even sunburned, despite the use of sunscreen, be sure to apply it sooner, before your child goes outside, apply much more (consider using 2 to 4 times more sunscreen), reapply it much more often, and consider using a high SPF sunscreen (SPF 100+) that is very water-resistant and offers broad-spectrum UVA and UVB protection.

Sources

Auerbach: Wilderness Medicine, 5th ed.

CDC. Skin Cancer Prevention April 2010.

FDA. Sunburn Protection Factor (SPF). April 2009.

Kim SM. The relation between the amount of sunscreen applied and the sun protection factor in Asian skin. J Am Acad Dermatol - 01-FEB-2010; 62(2): 218-22.

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