Linear and exponential sunscreen behaviours as an explanation for observed discrepancies in sun protection factor testing

Visual Aids for Sunscreen Application: A mixed methods study

BACKGROUND

Consumers routinely underapply sunscreen, and this may be because they misinterpret application quantity directions on sunscreen labels. U.S. labels use ambiguous terms such as "apply generously" to communicate application quantity. Visual aids may be helpful to consumers to determine proper application quantity.

PURPOSE

To examine sunscreen application practices and sunscreen quantity visual aid preferences.

METHODS

Sets of five GIFs and five static images were created corresponding to five quantities of sunscreen. Participants extracted their typical-use sunscreen quantity from a pre-measured tube and answered questions about their estimation process and use of labeled instructions. Participants then identified their typical-use sunscreen quantity in response to three stimuli: teaspoons, images, and GIFs and reported their preferred format.

RESULTS

No participants reported using the label directions for application quantity to inform their sunscreen use. The GIF-based visual aid for sunscreen application quantity (44%) was preferred over image-based (40%) or teaspoon-based (16%) versions (p = .0249). Addition of a GIF demonstration to clarify application quantity was reported as highly helpful.

CONCLUSION

Consumers have difficulty determining the appropriate quantity of sunscreen to use and labeling does not influence their application quantity. A QR code incorporating an image or GIF demonstration of proper sunscreen quantity could be useful to sunscreen consumers.

[Sunscreens of the future: challenges and opportunities]

Sunscreens provide excellent protection against erythema and against chronic damage such as photoaging and skin cancer. Today's challenges concern safety of the products and improved methods for standardizing the evaluation of their efficacy. Other important topics are the further development of sunscreen products, as well as personalization of use. Personalized sun protection based on the phenotype, the genetic profiles and moreover the skin's microbiome - all linked to the identification of certain consumer susceptibility factors - is an exciting new area of research. In particular, the expansion with innovative topical agents such as DNA repair liposomes in improved galenic formulations with UV filters tailored to the skin phototype and new topical antioxidants could in future provide even more comprehensive sun protection. New antioxidants and other agents such as nicotinamide could increase systemic photoprevention. Sustainability will also be an important aspect to protect consumers, but also the environment (i.e. especially marine wildlife) from toxic effects of sunscreens.

Laboratory testing of sunscreens on the US market finds lower in vitro SPF values than on labels and even less UVA protection

Background

New research has attributed increased significance to the causal link between ultraviolet A (UVA) radiation and immunosuppression and carcinogenesis. In the United States, sunscreens are labeled with only their sun protection factor (SPF) and an imprecise term “broad‐spectrum protection.” Sunscreen marketing and efficacy evaluations continue to be based primarily on skin redness (sunburn) or erythema. We sought to evaluate the ultraviolet (UV) protection offered by common sunscreen products on the US market using laboratory‐measured UV‐absorption testing and comparing with computer‐modeled protection and the labeled SPF values. This approach enables an investigation of the relationship between the labeled SPF and measured UVA protection, a factor that is ignored in current regulations.

Methods

Fifty‐one sunscreen products for sale in the United States with SPF values from 15 to 110 and labeled as providing broad‐spectrum protection were tested using a commercial laboratory. All products were evaluated using the ISO 24443:2012 method for sunscreen effectiveness. The final absorbance spectra were used for analysis of in vitro UV protection.

Results

In vitro SPF values from laboratory‐measured UV absorption and computer modeling were on average just 59 and 42 percent of the labeled SPF. The majority of products provided significantly lower UVA protection with the average unweighted UVA protection factor just 24 percent of the labeled SPF.

Conclusion

Regulations and marketplace forces promote sunscreens that reduce sunburn instead of products that provide better, more broad‐spectrum UV protection. The production and use of products with broad spectrum UV protection should be incentivized, removing the emphasis on sunburn protection and ending testing on people.

Photoprotection of the future: challenges and opportunities

The use of sunscreens is an important and essential component of photoprotection. Since their introduction during the first half of the last century, sunscreens have benefited enormously from major technological advances such as the development of novel UV filters; as a result, their efficacy in preventing UV-induced erythema is unequivocal. More recently, however, new challenges have appeared, which have prompted a robust discussion about the safety of sunscreens. These include topics directly related to photoprotection of human skin such as improved/alternative methods for standardization of assessment of the efficacy of sunscreens, but also many others such as photoprotection beyond UV, concerns about human toxicity and ecological safety, the potential of oral photoprotective measures, consequences of innovative galenic formulations. On a first glance, some of these might raise questions and doubts among dermatologists, physicians and the general public about the use sunscreens as a means of photoprotection. This situation has prompted us to critically review such challenges, but also opportunities, based on existing scientific evidence. We conclude by providing our vision about how such challenges can be met best in the future in an attempt to create the ideal sunscreen, which should provide adequate and balanced protection and be easy and safe to use.

Linear and exponential sunscreen behaviours as an explanation for observed discrepancies in sun protection factor testing

Background

In vivo testing of sun protection factor (SPF) values can show considerable interlaboratory variability. We studied the underlying reasons and clinical implications.

Methods

Following the ISO 24444:2010 SPF testing method, seven contract research organizations (CROs) tested eight sunscreens marketed as SPF50 or SPF50+ and the reference SPF15 sunscreens P2 and P3 and SPF43 P6. We analysed differences in the products and CRO testing methods with regard to SPF variability. We tested the erythema prevention capacity of five of the products in subjects exposed to high doses of natural sunlight in Mauritius.

Results

Sun protection factor values varied dramatically between different CROs for some, but not all of the sunscreens. Those with the largest variability had an SPF50+, and their SPF values differed from a maximum of 62.4 to a minimum of 5.5. These products did not share a common sun‐filter composition, and some CROs used low and others high irradiation dose regimens. When comparing these two regimens, test products fell into two categories: (i) they either behaved similarly (“linear”) or (ii) they behaved differently (“exponential”). In the outdoor clinical study, exponential and linear sunscreens did not differ in their photoprotection capacities.

Conclusion

Differences in reported SPF values depend on the linear vs exponential behaviour of such products if subjected to low‐ vs high‐dose test regimens. Under real‐time exposure to natural sunlight, exponential and linear sunscreens did not differ in their erythema prevention capacity. Laboratory SPF testing of exponential sunscreens bears the risk of underestimating their in‐use SPF.