SPF indicates the length of time you can be in the sun without burning, but factors like sweating and water sports can strip away protection. SPF only measures UVB protection, while UVA rays are linked to skin aging and cancer. Chemicals like Parsol 1789 can block both UVA and UVB rays, but their long-term effects are unknown. Frequent application and avoiding the sun between 10am and 4pm are more important than the strength of the sunscreen. Doctors recommend SPF 15 or higher, but higher SPF may not be necessary if sunscreen is reapplied often.
The sun protection factor (SPF) represents the length of time you can be in the sun without burning, multiplied by the corresponding number. So a person who would normally begin to burn in 10 minutes could theoretically have 150 minutes of sun protection with a sunscreen that has an SPF of 15.
Regardless of the SPF number, the sunscreen test doesn’t really equate to the amount of time you can be in the sun without burning because sweating, clothes rubbing against your skin, and water sports will strip away the sun protection. The tests also use significantly more sunscreen than most people, so SPF number results can be inaccurate. Usually, a sunscreen with SPF 15 will give you about an hour of protection before reapplying sunscreen. This, of course, varies from person to person. It also helps to wear protective clothing, hats, and sunglasses.
The SPF number refers only to the protection from ultraviolet B (UVB) rays. Ultraviolet A (UVA) protection isn’t measured by these numbers and, until recently, was often unavailable in sunscreens. UVB rays are more powerful, quicker to produce sunburn, and have been linked to skin cancer. UVA rays are associated with skin aging and, together with exposure to UVB rays, can increase the risk or facilitate skin cancer. UVA although milder, is still not safe.
Certain chemicals found in newer sunscreens that also boast an SPF number can help block UVA rays. Chemicals like Parsol 1789 block both UVA and UVB rays. Unfortunately, these chemicals are of concern to environmentalists because they have been found in water, groundwater, and soil. The potential long-term effects of exposure are unknown.
What remains important to remember is that the strength of the sunscreen is less important than frequent application and avoiding the sun between 10am and 4pm, when UVB rays are strongest. Sunscreen should always be combined with protective clothing and sun protection during the hottest, brightest parts of the day.
Some people pay more for higher SPF protection, and that can make sense for those with lighter skin. Doctors generally recommend buying a sunscreen of 15 or higher. There are the lower ones, which will make your skin tan or burn in less than an hour. It may not be necessary to purchase a sun protection factor higher than 15, except perhaps for infants, if you can be careful to reapply sunscreen every hour and after swimming or very vigorous physical activity.
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