Sunscreen that doesn't wipe off for hours? Research highlights UVA substantivity

By Andrew MCDOUGALL contact

- Last updated on GMT

Typical evolution of Visiopor follicular fluorescent dots (a) before one application of a sunscreen, (b) immediately after application, and (c) a couple of hours later.
Typical evolution of Visiopor follicular fluorescent dots (a) before one application of a sunscreen, (b) immediately after application, and (c) a couple of hours later.

Related tags: Sun care products, Ultraviolet

Scientists in Belgium and Germany have shown how long sunscreen may resist removal once applied to the skin, showing that the effect of UVA blockers can last for a number of hours.

In the study, published in the Journal of Cosmetic Dermatology​, the team conclude that all UVA blocker-containing sun care products exhibited a similar overall quenching effect on porphyrin-enriched facial hair follicles and dermal fibres.

“This effect lasted for a few hours,”​ says the research. “Differences in the fluorescence recovery were likely related to the amount in sun care application and the nature of the formulation components.”

Measuring

Under specific light illumination, particularly ultraviolet radiation (UVR), the skin produces both specular light reflectance and, possibly, specific fluorescent emission.

A quenching effect of fluorescence is observed following the application of sunscreens active against UVA radiations.

In this study the team, made up from scientists at the University of Liège and 2CK Electronic in Cologne, assessed noninvasively in a real-time process, the potential sunscreen remanence/substantivity after application on the skin.

To do this they used a Visiopor device in a real-time procedure after application of sunscreens to the skin, and a quenching effect of follicular fluorescence due to bacterial porphyrins was also evaluated at 30 minute intervals.

A Visioscan device was then used as a distinct UVA emitter in a control procedure of spectral analysis of specular UVR emission and reflectance by dermal fibres.

“The presently described method is cheap, rapid, and noninvasive,”​ say the research team.

“It possibly fits with some specific questions including comparisons between distinct formulations, considerations about inter-individual differences, resistance to sweating and swimming, possible interactions with various topical formulations, influences of formulations on compliance, methods of applications, etc.”

The results of the tests showed that under UVA-1 irradiations, facial skin produced different patterns of specular UVR reflectance and fluorescent emission as well.

The porphyrin-related follicular fluorescence was instantly abated by UVA blockers present in sun care products, and the potential sunscreen remanence/substantivity was assessed by the follicular and inter-follicular fluorescence recurrence all along the next hours.

UVR exposure

A growing part of the Western populations, essentially Caucasian people, has increased the lifetime solar ultraviolet radiation (UVR) exposure following the expansion of the growing outdoor leisure time.

Over recent years, a greater awareness of the potential harmful effects of solar irradiation has emerged among scientists, physicians, and the lay public.

People are now aware that excessive solar radiations without appropriate protection are harmful and cause lesions including sunburn, photo-ageing, and skin cancers.

Sun care brands aim to decrease or in part control some of the UVR harmful effects on the skin, and decreasing skin exposure can reduce specific photo-damages including photo-ageing and photo-carcinogenesis.

In this field, UVA light is important to be considered in the whole spectrum of UVR.

Related topics: Formulation & Science, Skin Care

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