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All About Sunscreen

How to Properly Apply Sunscreen

How Much Sunscreen to Apply

What is SPF?

SPF stands for Sun Protection Factor. The number is determined experimentally indoors by exposing humans to a light spectrum meant to mimic noontime sun.

For example, a sunscreen with an SPF Of 15 filters 92% of the UVB (ultraviolet B, or the sun’s shortwaves) and allows a person to stay out in the sun 15 times longer than without using sunscreen. In other words, SPF 15 delays the onset of a sunburn in a person who would otherwise burn in 10 minutes to burn in 150 minutes.

There is currently no uniform measure of UVA (sun’s long-wave) absorption. There are broad-spectrum sunscreens that protect against UVA and a UVB radiation although it is important to remember that the SPF does not predict UVA protection. The UV Index is a public health education tool reported by meteorologists in 58 U.S. cities. It offers a daily report of UV light levels on a scale from 1-10+.

How Sunscreen Works

The Skin Cancer Foundation has some great information on the differences between UVA and UVB rays.

How can clothing help protect against SPF?

The protection clothing offers can also be measured by SPF. When you wear hats, sunglasses, long sleeves and other protective clothing, you are taking additional measures to live sunsmart while being able to live a fun, active lifestyle.

The following are examples of SPFs for various types of clothing:

  • Nylon Stockings – SPF 2
  • Hats - SPF 3-6
  • Summer-weight clothing – SPF 6.5
  • White T-shirt - SPF 8
  • Sun-protective clothing – up to SPF 30

Check out the Shop SunSmart store for additional protective gear. All proceeds go toward the Live SunSmart Foundation!

How to apply Sun Screen correctly - U and Your Skin

5 things you didn’t know about sunscreen


1. You need another coat.

“The general rule is a shot full for our entire body. But if you are in a bathing suit, that may not be enough,” according to dermatologist Cheryl Karcher

2. SPF isn’t everything.

The number gauges how well a sunscreen fends off UVB light, but not UVA rays. To ensure your sunscreen protects against both, scan the label for the word broad spectrum and more than one of the following ingredients: avobenzone (Parsol 1789), Mexoryl, titanium dioxide or zinc oxide.

3. Sunscreen weakens when exposed to heat and light.

Store your sunscreen in a cool place, not in the trunk of your car. Get sunscreen with stabilizing ingredients, like Helioplex or Dermaplex.

4. You may need to wear sunscreen indoors.

Unless they’ve been specially treated, the windows of your home or office typically won’t shield you from damaging rays, says dermatologist Francesca Fusco.

5. And underneath your clothes.

The average white cotton T-shirt provides an SPF of 10 or less. You may be better off putting a layer of sun screen on even under your clothing for added protection.

How to Apply Sunscreen

Additional links and resources

Know your UV levels and risks with this UV Safety Poster.

Get the facts. The CDC has a great facts sheet about skin cancer throughout the United States. Download this skin cancer fact sheet.

FDA Sheds Light on SPF and SunScreen - Important Information

Sunscreen - Stronger Rules - Better Protection FDA Video

Web MD (

eMedicine (

The Dermatology Group ( (

The Princeton Center for Dermatology (