Pharmacodynamic Modeling of Sunscreens: Efficacy Evaluation, Melanoma Incidences and Very Low to Very High Sun Protection Factor

Abstract

Pharmacodynamic modeling of sunscreens was performed using a new concept of Skin UV Index (SUI) on the exposed skin as a parameter to evaluate the potential effectiveness of sunscreens against sun damage.The SUI predicts the UV heat intensity on the skin surface in terms of the solar UV Index at the time of the study and is calculated by solar UV Index/sunscreen's SPF. SUI numbers for sunscreen with SPF ranging from 2 to 100 under a solar UV Index of 10 was used for illustration. Based on guidelines from WHO, Australia and New Zealand, sunscreens yielding SUI < 3 are assumed to be effective against sun damage such as sunburn and melanoma. Based on the above assumption, sunscreens with SPF > 4 were found to be effective when sunscreens were evenly applied at 2 mg/cm 2 . Review of numerous studies suggests that missing applications may represent a major, seemingly unavoidable, SPF-independent factor causing unintended sunburns for sunbathers in the US and other countries with a temperate climate. This might in turn become a major factor for causing exponential increase in melanoma incidence rates observed in the last few decades. For example, in an SPF 30 sunscreen study all 25 participants suffered unintended sunburns after one week of sunbathing. Also, a mean missing application of 20% of the total exposed area and a mean missing of about 50% of the time were reported in two separate studies. Simulations were also performed with under-applications of 50% and 75%.The present simulations may provide a rationale of why routine use of a low SPF 8 sunscreen was reported to be effective against melanoma in a 2018 Australian study. Based on model simulations it is proposed that in the US, SPF 8 sunscreen and SPF 2 to 6 sunscreen may be adequate for routine, unintentional use for sun-sensitive populations and non-sun-sensitive populations, respectively.

Perspectives on the FDA’s Sunscreen Policy: New Aging Theory, Sunlight Benefits, Enhanced Immunity, COVID-19 Mortality, Modelling Analyses, Melanoma Risks and Etiology

“…The topical use of propylene glycol, an FDA-approved calorie-generating nutrient, could quickly promote growth of tissues such as hair, nail, skin and gums apparently through the rejuvenation of each tissue's stem/progenitor cells [26] 2. The rejuvenation of hearts in old rodents could quickly produce unexpected systemic effects, reverse the aging process of hearts (including removal of scar tissue and repair of congestion), skin, hair, kidney and muscle and potentially increase the life span of rodents or humans [11,21,27] Exposure to excessive (UV Index, skin-sensitivity and time-length dependent) sunlight can obviously accelerate intrinsically induced aging symptoms such as age spots, wrinkles and sagging. In this new aging theory, formation of age or dark spots is attributed to born or acquired deficiencies in superficial microcirculation and formation of fine lines and wrinkles may result from a defense mechanism that could reduce the effective skin surface area to minimize its water loss [21].…”

“…A new Skin UV Index (SUI) was introduced recently [11]. It refers to sunlight heat intensity on the skin in terms of UV Index after sunscreen application.…”

“…i.e., 2 mg/cm 2 and the UV Index was 10 [11]. This suggests that for Caucasian white's use of these sunscreens may be effective against sunburn and melanoma and any reported inefficacies of sunscreens may be mainly attributed to various degrees of noncompliance with the label instruction [11]. SUIs were also estimated when only 50% and 25% of labelled amounts were applied as they may often occur in the real world [11].…”

“…This suggests that for Caucasian white's use of these sunscreens may be effective against sunburn and melanoma and any reported inefficacies of sunscreens may be mainly attributed to various degrees of noncompliance with the label instruction [11]. SUIs were also estimated when only 50% and 25% of labelled amounts were applied as they may often occur in the real world [11]. The present modelling analysis may thus provide a novel rationale as to why regular use of an SPF 8 sunscreen was effective against melanoma in Australia [60].…”

“…In the U.S., the non-whites presently account for about 40% of the population and may become the majority in 2050 [9,10]. Also, until recently no pharmacodynamic modelling studies regarding dosing evaluation have ever been published, although this kind of study has been generally required for new drug development and approval [11]. In this regard, some organic sunscreens were unexpectedly found to be significantly absorbed into the body, triggering the requirement for safety studies [12].…”