Sheera LaBelle, R.N.
University Health Services
The amount of ultraviolet radiation that strikes the earth’s surface (and you) depends on several factors:
1. Time of day: Maximum exposure occurs between 10 a.m. and 2 p.m.
2. Season: Intensity is much greater in summer but it is important to use sunscreen year-round.
3. Altitude: UV radiation increases 4 percent per 1,000 feet elevation. So at 5,000 feet there is 20 percent more radiation than at sea level.
4. Cloud cover: A thin cloud cover reduces UV radiation by only 20 – 40%.
5. Reflection: Reflected UV radiation is as damaging as direct.
6. Sand/concrete Reflects 25 percent of UV radiation.
7. Water Reflects up to 100 percent of UV radiation.
8. Snow Reflects 85 percent of UV radiation.
Protection is your best bet to reduce your risk of skin cancer and photoaging.
First, always apply sunscreen-at least SPF-15, 20 minutes before sun exposure, and reapply after sweating or getting wet.
Hats can protects the sensitive skin of the face and neck. A 4-inch brimmed hat reduces sun exposure to the head, neck and face by 70 percent.
Clothing is an important consideration as well. A white, dry cotton shirt provides a SPF of about 8, more protection if the fabric is dyed or thicker. Wet clothing allows 50 percent transmission of UV radiation.
UVA vs. UVB rays
UVA’s longer-wavelength rays can damage the skin’s connective tissue, leading to premature aging as well as playing a role in causing skin cancer. UVA rays also increase the risk of cataracts and retinal damage and are the type used in tanning salons. UVB radiation has shorter wavelengths and is primarily responsible for sunburn and skin cancer.
Which SPF is right For you?
Sun protection factor, or SPF, refers to a sunscreen’s ability to protect against the burning effects of UVB radiation. The higher the SPF, the longer you can be in the sun before you burn. If you normally burn after 10 minutes, a sunscreen of SPF 15 will allow you to remain in the sun 15 times longer before burning, or 150 minutes. Special conditions such as high altitude, tropical climates and reflective surfaces such as water, sand and snow may decrease this time. For routine, daily protection, a sunscreen with SPF 15 is adequate. You may want to use a higher SPF if you are very sun-sensitive or taking a drug that makes you burn more readily, such as tetracycline, a sulfonamide or a thiazide diuretic. Kids need a SPF of 30 to 45, since they spend so much more of their time in the sun. It is also estimated that 80 percent of one’s lifetime sun exposure occurs in childhood.
Do you need a “broad spectrum” sunscreen?
While UVB is responsible for the burning effects from the sun, both UVB and UVA can cause skin cancer. Furthermore, UVA rays penetrate more deeply into the skin and are responsible for prematurely wrinkled, aged skin and for drug-induced photosensitivity. Most products with SPF 15 or higher, and those labeled “broad spectrum,” adequately protect against UVA radiation. Shade UVAGuardr protects against all UVB and UVA. Sun blocks, which contain zinc oxide or titanium oxide, reflect sunlight and also protect completely against all UVA and UVB. While UVA protection is important for everyone, use the most UVA-protective sunscreens or sun blocks if you are in the sun for long periods on a daily basis, or are using photosensitizing medication.
Should you use “water-resistant” or “waterproof?”
Water is not a barrier to the sun’s rays. As much as 60-80 percent of UV radiation is transmitted through the first 12 inches of water in a pool. The law requires products labeled waterproof need only remain on water-immersed skin for 80 minutes, while water-resistant products need to be reapplied after as little as 40 minutes. There are some products that live up to their claim of all-day protection in water, but for most waterproof products, it is best to reapply every 90 minutes if you are sweating or swimming. Reapplying sunscreen will only restore, not extend, its protection.
How should you use sunscreen?
People with all but the darkest skin should use sunscreen every day, even when it’s cloudy. Apply sunscreen generously and evenly, at least 30 minutes before exposure. Don’t forget areas under sheer clothing or clothing that will be getting wet. Sunscreen can be applied under make-up or over other medicated skin products. Avoid use of products containing para amino benzoic acid derivatives (PABA) and discontinue use of your sunscreen if it causes redness, itching or rash.