Understanding the heat index and SPF

June 17, 2014


Jordan Smith

Zenith City Weekly


It’s summer! Time to hit the park or beach, or just chill out in the yard. Barbecues, field sports, and fireworks are the norm, but fun in the sun comes with dangers as well. Just like winter’s intense cold, summer heat needs to be treated with due respect.


In 1994, the National Weather Service and the Environmental Protection Agency developed an ultraviolet index to calculate the risk of sunburn. This index value began to be included in Weather Service forecasts.


The heat index was revised ten years later to make it consistent with guidelines of the World Health Organization and the World Meteorological Organization. It combines the air temperature and relative humidity.


High humidity does not actually affect air temperature, but it can make you feel hotter because it slows down the evaporation of perspiration on your skin, which cools you off. Dogs pant to keep cool; humans sweat for the exact same reason.


To account for this effect, the heat index reports the apparent temperature, rather than the actual temperature, and lists various danger zones by apparent temperature. However, since everyone is different, an “extreme caution” zone for one person could be an “extreme danger” zone for another.


If your local weather forecast moves the heat index into the “caution” zone, minimize your time outside and don’t exert yourself too strenuously.


Be sure to drink plenty of water. If you experience cramps in leg or abdominal muscles, it could be the first sign of overheating. Lie down in a cool location, massage cramped muscles, and keep drinking water. Avoid alcohol or sugary beverages when trying to beat the heat. Good old-fashioned H₂O is all you need.


Heat exhaustion is characterized by heavy sweating, weakness, pale and clammy skin, and possible fainting or vomiting. This is serious and requires attention.


Bring the victim out of the sun to lie down and sip water. Air conditioning is a huge plus at this point. If symptoms persist or worsen, seek medical attention.


Heatstroke is a medical emergency. Look for high body temperature, hot, dry skin, and a rapid, strong pulse. The victim may lose consciousness and should be brought to a hospital as soon as possible.


It’s also important to protect yourself from the sun at this time of year. Cover exposed skin in a sunscreen FDA approved as “broad spectrum,” which means it protects against both types of ultraviolet light—the kind that burns your skin (UVB) and the kind that can cause skin cancer (UVA).


The “sun protection factor,” or SPF, is supposed to tell you how much longer you can stay out in the sun than you could without it. For example, an SPF of 2 would mean you can stay out in the sun twice as long before getting sunburned. An SPF of 15 would mean you can stay out 15 times longer.


The trouble is, everybody’s skin responds differently to the sun. Generally, the darker your natural complexion, the safer you are, but an SPF of 70—which is available on the market—doesn’t mean you can stay out in the sun safely for 12 hours. Attempting to market higher and higher SPFs is starting to make the number meaningless.


It’s good to wear a high SPF sunscreen, but it’s more important to find one approved as broad spectrum. It’s most important to avoid prolonged sun exposure, take plenty of breaks, and drink plenty of water. Reapply sunscreen after swimming and during breaks. Your natural perspiration will wash it off.


“Waterproof” sunscreen is no longer allowed. It blocked natural perspiration and it didn’t really work. Sunscreens can be marketed as “water resistant,” but reapply those regularly anyway.


Sunburns are usually just unpleasant, but they can be dangerous. Burning can begin in less than 15 minutes, yet it might take you several hours to feel it, so you can get burned much worse than you realize before you even know it’s happening.


During our brief, gorgeous days of summer here in the Twin Ports, it may be easy to forget all about last winter, but sunburns are possible, even in January. There’s less sunlight and it’s not as high in the sky, but ice and snow reflect ultraviolet rays back at you and can burn you in the same way.


The rest of June looks to be four degrees below average, but July might be two degrees above average, which would be a first in quite some time. Watch for thunderstorms throughout the month. 

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