UV Radiation and Sunscreens

Exposure to ultraviolet (UV) radiation from the sun is the most common cause skin damage, including collagen disruption, free-radical formation, DNA repair interference, and immune-system inhibition. A few simple facts about UV radiation and sunscreens will help you to protect yourself.

UV radiation is classified depending on wavelength, which is measured in nanometers (nm):

UVC: 100 to 290 nm
UVB: 290 to 320 nm
UVA: 320 to 400 nm

UVC radiation from the sun does not reach Earth at appreciable levels (it can be generated artificially).It is not of concern to us in relation to skin damage.

UVB radiation causes sunburn by affecting the top layer of the skin, the epidermis (see A Brief Tour of the Skin). The intensity of UVB radiation corresponds to the intensity of sunlight: The highest levels occur in the middle of a summer day.

UVA radiation is considered to be the perpetrator of most extrinsic skin aging. The longer UVA rays penetrate the epidermis and affect the lower layers of the skin. The ambient level of UVA radiation is basically constant: Your skin can be damaged on a foggy winter morning. Unlike UVB, UVA rays penetrate glass.

Exposure to the UV radiation in sunlight ages your skin, causing wrinkles, blotches, and thinning. Fair skin is most vulnerable to damage, but all skin is affected. Proper use of a good sunscreen can protect your skin.

There are two types of sunscreens: physical and chemical. Physical blocks are effective for both UVA and UVB. The best known are titanium dioxide and zinc oxide, both of which are available in a clear (micronized) form. If your skin is particularly sensitive, you may want to look for a sunscreen that contains only one or both of these active ingredients.

Chemical blocks absorb either or both UVA or UVB radiation. Avobenzone (butyl-methyoxydibenzoylmethane; Parsol) is an effective broad-spectrum chemical block. Octyl methoxycinnamate, octyl salicylate, and oxybenzone are among the popular chemical blocks; effective products often use them in conjunction with avobenzone or physical blocking agents. PABA (para-aminobenzoic acid) was once a popular sunscreen ingredient, but it can be extremely irritating and most people now prefer to avoid it.

A minority of sunscreen labels state the range of wavelengths blocked or absorbed by each of their ingredients. That information is the most accurate, and allows you to assess whether the sunscreen adequately protects you from UVA and UVB. Learn to read labels carefully before you purchase any product that touches your skin!

Although the sun-protection factor (SPF) number is a helpful indicator, it does not give you sufficient information to choose a sunscreen. SPF is a measure of only UVB blockade; UVA blockade is at least as important. The SPF indicates how long you can stay in the sun before your skin is reddened and burned. The SPF number indicates by what factor you can multiply the protection that your natural skin affords. For example, say that you can expose your skin for 20 minutes without burning; perfect application of a sunscreen with SPF 15 theoretically will allow you to stay in the sun 15 times longer, or 5 hours.

Generally, you want a sunscreen to have an SPF of at least 15. The SPF is not a linear measure: A sunscreen with SPF 20 does not provide twice as much protection as one with SPF 10. In fact, there is little difference in protection, measured as percentage of radiation blocked, among products with SPF above 30. Rather, the difference lies in how long you can stay in the sun before your skin begins to burn.

Sunscreens also are formulated specifically for dry, oily, or blemish-prone skin, for facial use, and so on. Some are formulated for people who exercise vigorously or immerse themselves in water. Some are dual-duty sunscreens and moisturizers. Others combine tint, topical medication, or makeup foundation with sunscreen. If you choose makeup that boasts an SPF number, you may still want to apply sunscreen on top of it. Otherwise, you must apply a thick, even coating of makeup.

The amount of protection that a sunscreen provides is heavily influenced by how you use the product. Most people do not apply enough sunscreen to form an unbroken protective film. Because sunscreen is partially absorbed and disperses more evenly with time, you should apply it at least 20 minutes before you are exposed to the sun. In general, you should put on sunscreen over any other substance that you apply to your skin, such as moisturizer or foundation, so that you do not dilute the sunscreen. An exception is high-SPF loose powder, which you can use to set the sunscreen and to ensure a matte finish. Finally, you must reapply sunscreen often. Use common sense. If you are swimming, exercising vigorously, or toweling yourself dry in full sunlight, you will need to reapply your sunscreen more often than if you are working indoors and occasionally passing a sunlit window. Err on the side of caution. If your face starts to feel heavy with sunscreen, such as when the sunscreen loads up with dust or grime, just rinse off, blot dry, and start fresh.

Make sunscreen application part of your daily routine, all year round. In the morning, and as appropriate throughout the day, apply your sunscreen, regardless of how much time you expect to spend outside. Although clothing that covers more skin rather than less also provides a measure of protection, be aware that your skin can be damaged through fabric too.

Various cosmetic treatments and topical or oral medications can make your skin even more vulnerable to the damaging effects of UV radiation. Wendy will teach you how and when to apply extra protection. She can also recommend the highest-quality sunscreens most suited for your particular skin type. You can purchase these superb products from Wendy’s Store.