The trouble with SPF

Curated by Claudia Shannon / Research Scientist / ishonest

Most consumers choose a sunscreen product based on its sun protection factor, or SPF, often reaching for products with a high SPF value, assuming they offer the best protection from the sun’s harmful ultraviolet, or UV, rays. But that is often far from the truth.

SPF values are an unreliable measure of the effectiveness of sunscreens. A good sunscreen will provide equal broad-spectrum protection against both UVA and UVB rays. However, the SPF value reflects only how well a product will protect from UVB rays, the main cause of sunburn and non-melanoma skin cancers, such as squamous cell carcinoma (von Thaler 2010). SPF values do not reflect a product’s ability to protect from other harmful UV rays, such as UVA, which penetrate the skin more deeply and are associated with skin aging and cancer. SPF values are also unreliable because the test method companies are required to use to determine a product’s SPF value is imprecise. The test methods require someone to determine a change in the skin redness of a small handful of human participants exposed to UV light in a lab. These results may differ based on the evaluator, testing instrumentation or participant skin type. And SPF testing conditions used for labeling significantly overestimate the protection provided in actual use outdoors.

One study highlighted the potential for variability in SPF. When Procter & Gamble tested a competitor’s SPF 100 product at five different labs, the results varied from SPF 37 to SPF 75. A 1.7 percent difference in light transmission yielded an SPF measurement of 37 instead of 100. The company concluded that a very small difference in test conditions could dramatically affect the calculated SPF. Small differences in application thickness could have a similar effect. Because of the way SPF values are calculated, these errors would be most dramatic for high-SPF products.

Products with SPF values greater than 50+ also tend to give users a false sense of security. High SPF sunscreens not only overpromise protection but, according to the Food and Drug Administration, may also overexpose consumers to UVA rays and raise their risk of cancer. Many studies have found that people are more likely to use high-SPF products improperly and, as a result, may expose themselves to more harmful ultraviolet radiation than do people who rely on products with lower SPF values.

People trust these high SPF products too much.

There are four key strikes against SPF values greater than 50+. They include:

1. Poor balance. A sunscreen’s SPF rating has little to do with its capacity to shield the skin from UVA rays. As SPF increases, the ratio of UVA protection decreases. High-SPF products suppress sunburn much more effectively than they protect from UVA-induced damage, like suppression of the immune system, formation of harmful free radicals in skin, and development of melanoma. As a result of inadequate UVA standards and limited options for providing UVA protection, U.S. sunscreens offer far less protection against UVA than UVB rays, and this is worst for products with the highest SPF values.

2. Consumers misuse high-SPF products. High-SPF products tend to lull users into a false sense of security, so they stay in the sun longer and overexpose themselves to both UVA and UVB rays well past the point when users of low- SPF products would head indoors. As a result, they get as many UVB-inflicted sunburns as unprotected sunbathers and are likely to absorb more damaging UVA radiation.

Philippe Autier, a scientist formerly at the World Health Organization’s International Agency for Research on Cancer, has conducted many studies of sunbathers and believes that high-SPF products spur “profound changes in sun behavior” that may account for the increased melanoma risk found in some studies. In two studies, Autier confirmed that European vacationers spent more total time in the sun if they were given an SPF 30 instead of SPF 10 sunscreen (Autier 1999, 2000). We assume the difference would also apply to products with SPF values greater than 50.

3. Sunburn protection that is only marginally better. Sunbathers often assume they get twice as much protection from SPF 100 sunscreen as from SPF 50. But the extra protection is negligible. Properly applied SPF 50 sunscreen blocks 98 percent of UVB rays; SPF 100 blocks 99 percent. When used correctly, sunscreen with SPF values between 30 and 50 offers adequate sunburn protection, even for people most sensitive to sunburn.

4. High-SPF products may pose greater health risks. High-SPF products require higher concentrations of sun-filtering chemicals than low-SPF sunscreens do. Some of these ingredients may pose health risks when they penetrate the skin and have been linked to tissue damage and potential hormone disruption. Some may trigger allergic skin reactions. If studies showed that high-SPF products were better at reducing skin damage and skin cancer risk, the extra chemical exposure might be justified. But they don’t, so choosing sunscreens with lower concentrations of active ingredients – SPF 30 instead of SPF 70, for example – is prudent.

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