Mari K. Hopper, PhD
Associate Dean for Biomedical Science
Sam Houston State University College of Osteopathic Medicine

Disruption sparks creativity and innovation. For example, in hopes of curbing viral spread by moving classroom instruction outdoors, one Texas University recently purchased “circus tents” to use as temporary outdoor classrooms.

Although circus tents may be a creative solution… solving one problem may inadvertently create another. Moving events outdoors may be effective in reducing viral spread, but it also increases the skin’s exposure to harmful ultraviolet (UV) radiation from the sun. The skin, our body’s largest organ by weight, is vulnerable to injury. For the skin to remain effective in its role of protecting us from pollutants, microbes, and excessive fluid loss – we must protect it.

It is well known that UV radiation, including UVA and UVB, has deleterious effects including sunburn, premature wrinkling and age spots, and most importantly an increased risk of developing skin cancer.

Although most of the solar radiation passing through the earth’s atmosphere is UVA, both UVA and UVB cause damage. This damage includes disruption of DNA resulting in the formation of dimers and generation of a DNA repair response. This response may include apoptosis of cells and the release of a number of inflammatory markers such as prostaglandins, histamine, reactive oxygen species, and bradykinin. This classic inflammatory response promotes vasodilation, edema, and the red, hot, and painful condition we refer to as “sun burn.”^1,2

Prevention of sunburn is relatively easy and inexpensive. Best practice is to apply broad spectrum sunscreen (blocks both UVA and UVB) 30 minutes before exposure, and reapply every 90 minutes. Most dermatologists recommend using SPF (sun protection factor) of at least 30. Generally speaking, an SPF of 30 will prevent redness for approximately 30 times longer than without the sunscreen. An important point is that the sunscreen must be reapplied to maintain its protection.

There are two basic formulations for sunscreen:  chemical and physical. Chemical formulations are designed to be easier to rub into the skin. Chemical sunscreens act similar to a sponge as they “absorb” UV radiation and initiate a chemical reaction which transforms energy from UV rays into heat. Heat generated is then released from the skin.³  This type of sunscreen product typically contains one or more of the following active ingredient organic compounds: oxybenzone, avobenzone, octisalate, octocrylene, homosalate, and octinoxate. Physical sunscreens work by acting as a shield. This type of sunscreen sits on the surface of the skin and deflects the UV rays. Active ingredients zinc oxide and/or titanium dioxide act in this way.⁴  It’s interesting to note that some sunscreens include an expiration date – and others do not. It is reassuring that the FDA requires sunscreen to retain their original “strength” for three or more years.

In addition to sunscreen, clothing is effective in blocking UV skin exposure. Darker fabrics with denser weaves are effective, and so too are today’s specially designed fabrics. These special fabrics are tested in the laboratory to determine the ultraviolet protection factor (UPF) which is similar to SPF for sunscreen.  A fabric must carry a UPF rating of at least 30 to qualify for the Skin Cancer Foundation’s Seal of Recommendation. A UPF of 50 allows just 1/50th of the UV rays to penetrate (effectively blocking 98%). Some articles of clothing are produced with a finish that will wash out over time. Other fabrics have inherent properties that block UV rays and remain relatively unchanged due to washing (some loss of protection over time is unavoidable) – be careful to read the clothing label.

Some individuals prefer relying on protective clothing instead of sunscreen due to concerns about vitamin D synthesis. Vitamin D activation in the body includes an important chemical conversion stimulated by UV exposure in the skin – and there is concern that sunscreen interferes with this conversion. However, several studies, including a recent review by Neale, et al., concluded that use of sunscreen in natural conditions is NOT associated with vitamin D deficiency.5,6 The authors did go on to note that at the time of publication, they could not find trials testing the high SPF sunscreens that are widely available today (current products available for purchase include SPFs over 100).

Additional concern about use of sunscreens includes systemic absorption of potentially toxic chemicals found in sunscreen. A recent randomized clinical trial conducted by Matta and colleagues investigated the systemic absorption and pharmacokinetics of six active sunscreen ingredients under single and maximal use conditions. Seven Product formulations included lotion, aerosol spray, non-aerosol spray, and pump spray. Their study found that in response to repeat application over 75% of the body surface area, all 6 of the tested active ingredients were absorbed systemically. In this study, plasma concentrations surpassed the current FDA threshold for potentially waiving some of the additional safety studies for sunscreen. The authors went on to note that the data is difficult to translate to common use and further studies are needed. It is important to note that the authors also conclude that due to associated risk for development of skin cancer, we should continue to use sunscreen.

Yet another concern for using sunscreen is the potential for harmful environmental and human health impact. Sunscreen products that include organic UV filters have been implicated in adverse reactions in coral and fish, allergic reactions, and possible endocrine disruption.8,9 In some areas, specific sunscreen products are now being banned (for example, beginning January of 2021, Hawaii will ban products that include oxybenzone and octinoxate). As there are alternatives to the use of various organic compounds, there is a need to continue to monitor and weigh the benefit verses the potential negative effects.

Although the use of sunscreen is being questioned, there is the potential for a decline in use to be associated with an increase in skin cancer. Skin cancer, although on the decline in recent years, is the most common type of cancer in the U.S. It is estimated that more than 3 million people in the United States are diagnosed with skin cancers each year (cancer.net). Although this is fewer than the current number of Americans diagnosed with COVID-19 (Centers for Disease Control and Prevention, July 20, 2020) – changes in human behavior during the pandemic (spending more time outdoors) may inadvertently result in an increase in the number of skin cancer cases in future years.  

While we responsibly counter the impact of COVID-19 by wearing masks, socially distancing, and congregating outdoors – we must also continue to protect ourselves from damaging effects of the sun. As physiologists, we are called upon to continue to investigate the physiological impacts of various sunscreen delivery modes (lotion, aerosol, non-aerosol spray, and pumps) and SPF formulations. We are also challenged to investigate inadvertent and potentially negative impacts of sunscreen including altered Vitamin D metabolism, systemic absorption of organic chemicals, and potentially adverse environmental and health outcomes.

Again, solving one problem may create another challenge – the work of a physiologist is never done!

Stay safe friends!

Mari

References:

1. Lopes DM, McMahon SB. Ultraviolet radiation on the skin: a painful experience? CNS neuroscience & therapeutics. 2016;22(2):118-126.
2. Dawes JM, Calvo M, Perkins JR, et al. CXCL5 mediates UVB irradiation–induced pain. Science translational medicine. 2011;3(90):90ra60-90ra60.
3. Kimbrough DR. The photochemistry of sunscreens. Journal of chemical education. 1997;74(1):51.
4. Tsuzuki T, Nearn M, Trotter G. Substantially visibly transparent topical physical sunscreen formulation. In: Google Patents; 2003.
5. Passeron T, Bouillon R, Callender V, et al. Sunscreen photoprotection and vitamin D status. British Journal of Dermatology. 2019;181(5):916-931.
6. Neale RE, Khan SR, Lucas RM, Waterhouse M, Whiteman DC, Olsen CM. The effect of sunscreen on vitamin D: a review. British Journal of Dermatology. 2019;181(5):907-915.
7. Matta MK, Florian J, Zusterzeel R, et al. Effect of sunscreen application on plasma concentration of sunscreen active ingredients: a randomized clinical trial. Jama. 2020;323(3):256-267.
8. Schneider SL, Lim HW. Review of environmental effects of oxybenzone and other sunscreen active ingredients. Journal of the American Academy of Dermatology. 2019;80(1):266-271.
9. DiNardo JC, Downs CA. Dermatological and environmental toxicological impact of the sunscreen ingredient oxybenzone/benzophenone‐3. Journal of cosmetic dermatology. 2018;17(1):15-19.
   
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