April's Health Genie: Sunscreen
Dear Health Genie,
Every year I buy several different sunscreens thinking one may be better than the other. Even though I work outside, I end up with extra tubes left at the end of the summer. Some sunscreen has irritated my face but I didn’t have any way of knowing this until I’d purchased it. Now I choose a baby sunscreen because it doesn’t make me itchy or one for faces or one that sprays on because those feel lighter. I enjoy being tan so I choose a low or medium SPF, skip sunscreen some days, and around midsummer I stop using sunscreen except on the very brightest days. Is that ok once I am tan? Sometimes people who see my dark tan warn me that I should always cover up even if I don’t think I am getting burned. Is it safe to continue using the sunscreens I bought last year, this year? Will you advise me about what to look for on the label? I know about SPF. What else should I know?
Thanks,
Outdoorsy Sun Lover
Dear Outdoorsy,
Let’s start with the basics. SPF stands for “sun protection factor.” When properly applied, SPF is a measure of how many times longer a person can stay in the sun before their skin burns. For example, if you would normally burn in 10 minutes then a sunscreen with SPF 15 would theoretically allow you to be in the same light for 150 minutes before beginning to burn. It’s important to remember that even with a high SPF sunscreen applied all day, the accumulative exposure over the course of a day can cause burning.
Your observation that your tan protects you from burning is correct, to an extent. A tan is considered to have a small degree of SPF. However, there is more to sun exposure and skin health than meets the eye. SPF indirectly measures protection from UVB rays. We are exposed to another range of wavelengths, called UVAs, that also affect our skin. While UVAs are not the chief cause of sunburns, they are associated with wrinkling and skin cancer. So it is true that even without any visible signs of a sunburn, your skin could still have sun damage.
Skin cancer and signs of aging are probably the main reasons to ensure proper use of sunscreen. Some brands now indicate UVA and UVB protection or claim “broad spectrum” on those products that protect against both of these types of UV rays. Symbols with “UVA/UVB”, “PA” and “UVA” all indicate protection against UVA rays. These symbols are used in Europe’s and Japan’s rating systems and soon the FDA will introduce a similar rating system in the United States.
There are two main categories of sunscreen protection, mineral and chemical. Mineral is the most traditional and uses zinc oxide and often titanium dioxide to reflect the sun’s rays. Chemical sunscreens are generally less whitening than zinc oxide sunscreens. New chemical sunscreens are developed regularly and the exact mechanism for protection depends on the chemical used. In general, the active ingredients in these sunscreens absorb the sun’s rays before they can damage the skin. Most chemical sunscreens utilize a number of active ingredients that may absorb different wavelengths of UV rays. Conversely, mineral sunscreens protect against a broad range of UV rays with one or two active ingredients. Mineral sunscreens begin to protect immediately, whereas chemical sunscreens may need to be absorbed into your skin for a period of time, usually 15 minutes, before actively protecting.
Chemical sunscreens expire in about a year because the active ingredients become inactive. The active ingredients in mineral sunscreens do not become inactive, but do fall out of dispersion. This means over time, the zinc and titanium won’t be evenly mixed in the lotion. Starting one year from the manufactured date, it is advisable to knead the tube or vigorously shake the bottle before use, and after two years discard it.
To respond to your comment about left over sunscreen, consider that you may not be applying enough. Make sure you read the instructions for the particular brand you’ve purchased. When you apply half as much as intended, you lower the SPF not by half but by the square root of the SPF on the label. Sunscreen labeled SPF 30 applied at half the thickness has an effectiveness of roughly SPF 5.5. So sunscreen applied incorrectly may give you a false sense of security while you’re enjoying the nice weather. To truly limit skin damage, it’s best to cover up and seek shady spots during hours when the sun is strongest (between 10am and 4pm).
Good Luck & Stay Protected!
The Health Genie
Sources:
- American Academy of Dermatology Sunscreens Page
- Skin Cancer Foundation UVA & UVB Information
- W.S. Badger Co. Sun Care Referenced PDF. 2012.