Do you know the difference between sunscreen and sunblock? How SPF ratings are determined? The difference between UVA and UVB rays? And how the sun interacts with free radicals to break down your skin's underlying support structures?

If you don't, you're jeopardizing your skin's health.

The Damage Can Be Extensive
And you have no way to estimate how much long-term damage your skin is suffering from sun exposure. The damage caused by solar radiation isn't limited to that blotchy, prune-like skin texture you see in elderly sun worshippers. Studies prove that early, repeated sun exposure is the No. #1 cause of skin cancer.

Free Radicals
How does the sun damage your skin?

In many ways. But one of the most serious, besides actually burning the epidermis to death (sunburn), is to create and stimulate free radicals. Free radicals (electrons seeking unstable atoms to bind with) damage cellular DNA by creating a war at the atomic level, destabilizing skin cells and degrading the molecules skin is made from.

This atomic war of attrition is at the root of the breakdown of collagen and other support structures of the skin.

Both UVA and UVB rays stimulate free radical proliferation.

UVA and UVB Rays
The sun emits energy over a large range of wavelengths. We call sun rays between 290 and 320 nanometers short UVB rays. We call sun rays between 320 and 400 nanometers long UVA rays.

UVB rays, the shorter rays, quickly burn the mid layers of skin. Within 15 minutes, these rays cause damage to cells, which will turn red within one hour. The damaged skin sends signals to the bottom layer of the epidermis, which responds by forming melanin inside the cells. Melanin is what makes the skin look "tan."

That so-called "healthy tan" people crave is actually a distress signal from your skin.

UVA rays, the longer rays, penetrate deeper into the skin and work more efficiently. Once they were thought to have a minor effect on skin damage. Recently they've been fingered as major culprits in skin damage.

Understanding the difference between these two toxic rays will help you make a wise decision about whether to apply sunscreen or sunblock to your skin.

• Sunscreens work by absorbing the energy of UV radiation before it affects your skin.
  
  Recent research has revealed that sunscreens are only truly effective on UVB rays. They offer almost no protection from UVA rays. Therefore, the SPF rating in a sunscreen is only a measurement of your protection from UVB rays. Label claims of Broad Spectrum or UVA protection are inaccurate and misleading.
  
  
• Sunblocks reflect or scatter UV radiation.
  
  Sunblocks give equal protection against UVA and UVB rays. Physical sunblocks use micronized titanium dioxide, equally effective against UVA and UVB rays.
  
  I recommend sunblocks over sunscreens, for obvious reasons.

SPF Rating
Sun Protection Factor (SPF) ratings indicate how long a sunscreen or sunblock remains effective on the skin. For instance, if you normally develop a sunburn in 10 minutes without wearing a sunblock, sunblock with an SPF of 15 will protect you for 150 minutes (10 minutes multiplied by the SPF of 15). A higher SPF means that you have greater protection and can therefore stay out in the sun longer.

Lotion, spray, gel - which works for you?
Sunblocks comes in a variety of forms: lotions, oils, sticks, gels, sprays and creams. We encourage you to try several types and find the one that works and feels the best to you.

All sunblocks should be applied 15-20 minutes before sun exposure, to allow a protective film to develop, then reapplied after water contact and sweating. Some sunblocks can lose effectiveness after two hours, so reapply frequently. In general, spray lotions and gels wash off more easily and need to be reapplied more frequently.

Frequent Application Is Important
How liberally you apply the sunscreen and how well it is able to set up generally have much more impact on the effectiveness of the application than the actual level of SPF.

One study showed that over 91% of the population put on about half as much sunscreen as is required by the FDA to qualify for the SPF level of protection. They overestimated the "staying power" of the sunscreen, did not reapply often enough, so their skin was exposed for short periods to the full strength of the sun's UVA and UVB rays.

The ability of the base mechanism to hold the sunscreen onto the skin is far more important to the sunscreen's performance than the SPF level.

Water Resistant and Waterproof
If you're out playing in the water, or perspiring heavily, determining how long a sunscreen or sunblock remains on the skin is very important. The FDA considers a product to be water-resistant if it maintains its SPF rating for at least 40 minutes of water exposure. To secure waterproof status, the FDA states that a product must maintain its SPF rating for more than 80 minutes of exposure.

Who's at Risk?
Spending long periods of time in the sun with non-protected, exposed skin is a recipe for disaster. Children are at greatest risk for sunburn due to their thin, sensitive skin. Remember that repeated exposure to the sun's ultraviolet radiation is the leading cause of skin cancer in later years.

Be Safe
The American Association of Dermatology (AAD) recommends that a "broad spectrum" sunblock with an SPF of at least 15 be applied daily to all sun exposed areas, then reapplied every two hours. However, in some recent clinical trials, sunblocks with SPF 30 provided significantly better protection than sunblocks with SPF15. To be safe, we recommend sunblocks with SPF of at least 30 with frequent reapplication.

To increase your safety in the sun you can also:

• Wear sun protective clothing
• Stay out of the sun from 10 a.m. to 3 p.m.

Be smart this summer. Don't jeopardize the beauty of your later years for a temporary look of "healthfulness." Now that you know the facts about sun protection, apply them.