Newsletter XXIII - Wearing SPF Sunscreen Properly

October is here with gray skies and cool winds. While long, heavyweight, layered clothing can provide excellent protection against UV radiation, the use of SPF sunscreen is vital to prevent sunburn during the winter. But it is important to apply sunscreen correctly.

A number of scientific studies have shown that when it is not used properly, sunscreen provides surprisingly little protection. Wright, Wright, and Wagner (Journal of the American Academy of Dermatology, May 2001) conducted a study of sunscreen use in Galveston, Texas. They found that sunscreen users often failed to cover all their exposed skin and to reapply sunscreen after activity. Because of these errors, 73% of sunscreen users in their study did not prevent sunburn.

It is also very important to apply the right thickness of sunscreen. Stokes and Diffey (Photodermatology, Photoimmunology, and Photomedicine, 1997) found an SPF 25 sunscreen only gave SPF 10 protection when two-thirds the recommended thickness was used, and SPF 5 protection when one-third the recommended thickness was used. They concluded, "Application thickness of sunscreen has a significant effect on the sun protection factor (SPF), with most users probably achieving an SPF of between 20% and 50% [of the label on the bottle or tube]."

Here are some tips for using sunscreen effectively during winter:

  • Use broad-spectrum sunscreen (blocks both UVA and UVB) with a rating of SPF 30 or higher on all unprotected skin, including lips, face, neck, ears, and hands.
  • Apply sunscreen 20 minutes before going outside, and reapply it every two hours while your skin is exposed to maintain the SPF level.
  • Apply sunscreen generously and evenly. During winter, use ¼ ounce for every application to cover your face, neck, ears, and hands.
  • Reapply sunscreen after perspiring heavily.
  • Throw away old sunscreen from summer. Sunscreens have an expiration date, and once that date is reached, products typically lose effectiveness.
  • Use sunscreen to block reflected UV. Keep in mind that snow reflects up to 80% of the sun's UVB rays!

And that brings us back to our cloudy October. I hope you establish a good sun-protection routine and remember to apply and reapply sunscreen as recommended. You'll help prevent sunburn, premature aging and skin cancer.