Five Sun Defenses – Part 3

As we have mentioned in a previous blogs, the five basic sun defenses that you should keep in mind when you go outdoors should include:

  • Avoiding peak hours of sunlight
  • Using sunscreen and/or sunblock
  • Selecting appropriate clothing
  • Keeping sunglasses handy
  • Seeking shade


In the last post we dealt with avoiding sunlight and sunscreen.  Today we will continue with using sunblock and selecting clothing.


“Physical” sunscreen ingredients lie on top of the skin and work by reflecting or scattering UV radiation. They are particularly useful for people who are sensitive or allergic to the ingredients found in other sunscreens.  Sunblocks often contain one or more of these ingredients:

  • Zinc oxide
  • Titanium dioxide
  • Iron oxide


Although past formulations were unsightly (often leaving a white film on the skin), newer “microfine” formulations are invisible after being applied.

Microfine titanium dioxide is effective at protecting from both UVA and UVB rays.

Water resistance – Sunscreens are classified as “water-resistant” if they maintain their protection after two 20-minute immersions in water. They are classified as “waterproof” if they maintain their protection after four 20-minute immersions. You should seek a water-resistant or waterproof sunscreen if you will be participating in water sports, such as swimming or water skiing, or will be actively sweating.

However, independent testing has shown many products do not perform well in the real world. So it remains a good idea to apply sunscreen every time you leave the water, or frequently if you are actively sweating.

Formulation – The formulation of a sunscreen or sunblock is important in that can determine if and when an individual actually applies the sunscreen.  Thick lotions that leave a film on the skin are not likely to be used repeatedly, so they may not be as effective as lotions, sprays or gels that dry quickly.  Choosing a formulation that is cosmetically acceptable to the individual using a sunscreen is paramount to successful use of the product.

Using a Sunscreen

Sunscreen should be applied evenly and liberally on all sun-exposed skin within 30 minutes before going outside to give sunscreen time to take effect. (Sunblocks are effective immediately after being applied.) Sunscreens should be reapplied every two hours or following swimming or sweating to ensure effective sun protection. Apply sunscreen generously and reapply frequently at least every two hours.

The chemicals may lose effectiveness over time, so it is important to throw away sunscreen that is past its expiration date or is over two years old.  No sunscreen is 100% effective; take additional measures to avoid the damaging effects of the sun’s rays.

In the next blog entry we will address using sunglasses and seeking shade…

Author: Jonathan S. Weiss, M.D.

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