HLTH-SUNSCREEN: Illustration of a bottle of suntan lotion boxing the Sun's rays. With Features story HLTH-SUNSCREEN. Alejandro Gonzalez, USA TODAY. 36p x 5-3/8'. Color. RGB JPEG image.
On the Saturday before Christmas, it rained at Disneyland.
Although it was cloudy just about all day, anyone trekking about, even with time logged inside a log flume or trinket store, would have received a bounty of sunshine. Maybe not enough to suffer a red-as-Lightning-McQueen burn, but a sufficient amount to bring that puffy, dazed feeling that accompanies too much sun.
It's not just a folk tale that you can get burned on a cloudy day: It's real. And people who spend any significant time outdoors any time of the year should remember to put on sunscreen and take other precautionary measures, even if the sky is hazy or overcast.
Scientists have known for decades that clouds can have a counterintuitive effect on sunshine. Ultraviolet rays beam from the sun and land on the Earth's surface, but clouds redirect them, refract them and generally bounce them around until they're seemingly everywhere. This can make it more dangerous for your skin, not less - an effect called "cloud enhancement."
There are two kinds of ultraviolet light: UVA and UVB. UVA is a longer-wavelength, deeper-penetrating sun ray that doesn't cause a burn but can still lead to skin cancer, as well as premature wrinkling and age spots. UVB is a shorter-wavelength ray that irritates the skin more immediately, leading to reddening and burning. Clouds block 70 percent to 90 percent of ultraviolet light, but not all. The thicker and darker the clouds, the less UV light comes through.
A 2006 article in American Scientist said every study since 1964 had shown some degree of cloud enhancement. For instance, measurements taken at the Mauna Loa Observatory in Hawaii in the 1990s showed a 29.8-percent increase in UVB light, compared with levels measured on clear days.
Of course, how well your skin handles the sun depends on how fair your skin is, as well as geographic factors: People who live closer to the equator get more sun exposure. Also, UV rays are most powerful at and around noontime; the time to avoid the sun is between 10 a.m. and 3 p.m.
The best advice for summertime also stands during winter: Use sunscreen, with an SPF of at least 15 (a max of 30 should be sufficient). Apply it 30 minutes before going outside. Shop for a product that is labeled "broad spectrum." This means it protects against both UVB and UVA rays. Sun protection factor (SPF) only applies to UVB.
"Even though clouds may block more than 50 percent of the UV rays, we just naturally don't think about sun protection as much," Dr. Matt Goodman, a dermatologist in the Melanoma Program at St. Joseph Hospital in Orange, Calif., wrote in an email. "And so, we leave our skin more exposed on a cloudy day, and this can result in a sunburn.
"So, better to protect our skin whenever we are outdoors - sunny or not!"