With growing awareness of ultraviolet (UV) exposure leading to increased risk of photoaging and skin cancers, consumers are using higher sun protection factor (SPF) sunscreens with frequent reapplication. New research, Evaluation of Reapplication and Controlled Heat Exposure on Oxybenzone Permeation from Commercial Sunscreen Using Excised Human Abdominal Skin, presented today at the 2018 American Association of Pharmaceutical Scientists (AAPS) PharmSci 360 meeting, demonstrates that heat and reapplication influence different sunscreen products containing the same amount of a key ingredient, oxybenzone, potentially affecting the safety and toxicity of UV filters included in sunscreens.
“What our research shows is that current safety testing procedures may underestimate the amount of oxybenzone absorbed through the skin given heat and reapplication, such as someone sunbathing. on the beach,” said presenting author Paige Zambrana, a graduate student in pharmaceutical sciences at the University of Maryland School of Pharmacy. “Although sunscreens are intended for the whole body at higher temperatures with reapplication every 80 minutes, safety testing to define UV filter limits only requires a single dose test at a temperature base skin temperature of 32 degrees Celsius.”
The researchers performed in vitro permeation tests, which indicated that oxybenzone, using both lotion and spray sunscreen formulations, was able to penetrate human skin with significantly higher cumulative permeation from the lotion. . With the addition of 24-hour heat exposure to the lotion, there was a 2.1-fold increase in cumulative oxybenzone permeation when comparing reapplication of sunscreen to 80 min and 160 min, at a single application and a 1.2-fold increase in permeation when comparing 24-hour heat application to 24-hour baseline temperature sunscreen reapplication studies. When comparing formulations, application of lotion with 24-hour heat and reapplication significantly increased cumulative oxybenzone permeation 3.1 times more than reapplication by spray.
“While sunscreen use is important and generally safe, our work suggests that some additional preclinical and clinical safety testing parameters should be considered before maximum UV filter levels are established,” noted Audra Stinchcomb, Ph.D., principal investigator and professor of pharmaceutical sciences. at the University of Maryland School of Pharmacy. “Additionally, given the potential environmental risks of oxybenzone and its recent banning in Hawaii, we focus on how different factors affect people to provide accurate predictions of total oxybenzone intake.”
The next step in this work will examine the use of sunscreens through controlled in vitro and in vivo test procedures with the eventual goal of establishing an in vitro-in vivo correlation between the two tests. In addition, clinical trials with currently marketed sunscreen products will be carried out to evaluate the conditions of use of sunscreens allowing a better understanding of the current maximum absorption of oxybenzone.
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