The Science of Sunscreen


The science behind sunscreen use may be more complicated than many consumers realize. Recently, a Seattle doctor spoke out against many of the potentially harmful characteristics of sunscreen, and told local Washington news station KING 5 television why some types of sunblock may be doing consumers more harm than good.

Dr. Jennifer Dietrich of Seattle claims that chemicals present in most sunblock can break down when exposed to light. However, claims like these are often based on ill-substantiated research. Many statistics and fact-sheets available to consumers, unfortunately, are presented with a big-business bias. How, then, can shoppers be sure that the chemicals in any given sunblock are safe?

For example, some consumer advocacy groups suggest that guidelines such as the SPF rating on the outside of a bottle of sunscreen may be misleading. Consumers should look for credible findings in medical journals and federally funded research organizations. Studies performed by outside organizations may be well intended, but results can be suspect when findings come from a subjective researcher.

Proctor & Gamble published the results of a test examining a competitor’s sunscreen, one that was labeled SPF 100. This lotion, assessed at five different laboratories, came back with results ranging from SPF 37 to SPF 75. The manufacturer claims that small variances in testing conditions can have a dramatic influence over the SPF calculation. Using sunscreens that falsely claim to give a higher SPF rating can cause shoppers to select the incorrect type of sunscreen for their outdoor activities. However intriguing studies like these may be, the results illustrate that research for labeling and for efficacy should be performed by outside labs and research institutions. Proctor & Gamble has a vested interest in discrediting its competitor. Therefore, more research should be conducted prior to drawing intelligent conclusions.

In addition to confusing labeling, chemicals inside sunscreen lotions were Dr. Dietrich’s primary concern in her talks with KING 5 News. Most sunscreen lotions available today, she said, are composed primarily of chemicals such as oxybenzone and octinoxate. This is true. Another controversial chemical found in sunscreens today is homosalate. Studies regarding these chemicals have been conducted for years.

Many medical journals have published findings that investigate claims regarding the danger of each of these chemicals listed. Over and over, studies have found that there is not enough conclusive evidence to suggest that any of these chemicals are particularly more or less effective either independently of or in combination with one another.

Research published in the Photochemical & Photobiological Sciences Journal in 2010 states specifically that absolutely none of these chemicals are harmful for adult consumers. An investigation published in the  Journal of American Medical Association Dermatology reiterated that fact.  “After 40 years of use,” the authors wrote, “we are not aware of any published study that demonstrates acute toxic effects in humans with systemic absorption of oxybenzone.”

Credible sources for scientific research claim that some of these chemicals have had measurable effects on test animals, altering both their hormone levels and reproductive function. Chemicals such as homosalate have been known to disrupt estrogen and progesterone function in women. A study published in the Journal of Investigative Dermatology reported that while disruptions in hormones for users have been observed, these disruptions are not necessarily harmful for adults. The results are inconclusive however, regarding children of differing ages and adolescents, and this is something that consumers might find interesting. This information however, is not considered to be sensational enough to capture the interest of the general public. For this reason, many claims about the science of sunscreen are exaggerated or manipulated with an end goal of selling more sunscreen.

The findings of nearly every private and public study suggest that what is important to individuals and their families is a matter of personal preference. Sunscreens approved by the Food and Drug Administration can be trusted to adequately block harmful rays from the sun when used as directed. This organization states that SPF 15 or higher is what consumers should shoot for.

User error, not necessarily exposure to harmful chemicals, constitutes the greatest danger to sunscreen users. Applying sunscreen incorrectly is the leading cause of sunscreen’s failure to protect its wearer. Sunscreen should be applied 15 minutes before exposure to the sun. It should also, according to the FDA, be re-applied every two hours. For good measure, this regulatory agency suggests that sun worshippers try to limit exposure between the hours of 10 a.m. and 2 p.m., when the suns rays are most intense.

In addition, consumers who use higher SPF sun lotions are often those who tend to spend longer periods of time exposed to direct sunlight. Without proper reapplication of sunblock, the risks for UV exposure are the same as if users had never applied any sunscreen at all. The FDA intimates that the foremost protection against prolonged sun exposure is to dress appropriately according to weather conditions, and to avoid spending large blocks of time in direct sunlight.

The FDA remind anyone planning to spend any time in the sun to choose sunscreen carefully. Using the wrong kind of sun protection, or using the right kind incorrectly, could do users more harm than good.

By Mariah Beckman

Photochemical & Photobiological Sciences
Journal of Biomedical Optics
Journal of American Medical Association Dermatology
Journal of Investigative Dermatology
Consumer Reports

One Response to "The Science of Sunscreen"

  1. Rick Hymer   October 6, 2014 at 1:12 pm

    Hi. Thanks for your article. I maintain a sunscreen blog called which means I do quite a bit of research on sunscreen. You are absolutely right that people not wearing sunscreen and/or not applying it correctly is the biggest concern.

    I get so aggravated with the EWG and the media and bloggers that perpetuate their public scares about sunscreen ingredients causing cancer, disrupting hormones, etc. The EWG is a well-funded special interest group whose top 12 or so executives/employees rake in half of the company’s annual donations. Any “consumer” organization that funnels that much money to management is up to much more than protecting us from evil corporate giants.

    If you like to ready my article on Oxybenzone, here you go…

    Thanks again for your sensible treatise on this important topic.

    R Hymer


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