Understanding Sun Protection and Sunscreens

In some ancient cultures, the sun was considered a deity, worshiped as the source of energy. The ancient Egyptians were the first civilisation noted to endeavour to photoprotect themselves with topical agents such as rice bran and jasmine. With the application of mineral sunscreen, they sought to achieve a lighter skin tone which was associated with higher socio‐economic status. Other attempted methods of photoprotection have been described in ancient Greek and Native American civilisations, which include the use of olive oil and extracts from coniferous trees.

UVR (Ultra Violet Radiation) was discovered in 1801 by Johann Wilhelm Ritter and, over a century later in the 1920s, scientists Karl Eilham Hausser and Wilhelm Vahle demonstrated the tanning effects of UVA exposure and sunburn that results from prolonged UVB exposure. This discovery led them to develop one of the first commercial sunscreens which comprised UVB filters; Benzyl Salicylate and Benzyl Cinnamate. Further sunscreens and filters emerged, including Eugene Shueller's Ambre Solaire by L’Oréal, which contained PABA.

In 1969, the photoaging effects of UVA were first described by the dermatologist Albert Kligman, who stressed the need for the development of UVA filters to be included in sunscreens. This was implemented a decade later, with Avobenzone as the first UVA filter. Currently, the sunscreen market continues to expand with more sunscreen formulations available.

A sunscreen is a product that protects the skin from radiation emitted by the sun. In Europe, these products are regulated by the European Commission, which regards them as cosmetic products. Whereas in the United States, products with photoprotective potential are regulated by the Food and Drug Administration (FDA) and are considered a drug. This means sunscreens are therefore subject to different regulatory and marketing requirements based on where they are retailed.

Sunscreens are categorised as either inorganic or organic, depending on the photoprotective component in the formulation. Organic sunscreens contain filters that absorb UVR before the skin does and convert it to thermal energy, which is then released from the skin. A filter is considered organic if it is carbon‐based and this does not equate to ‘natural’ nor do these filters decompose naturally in the environment. Inorganic sunscreens also protect skin by absorbing UVR, but they reflect visible light, which give them a more apparent appearance when applied.

The UVR filters in inorganic sunscreens include zinc oxide (ZnO) and titanium dioxide (TiO₂). Their large particles form a visible white cast on the skin, forming a physical barrier. This feature enables inorganic sunscreens to act as effective UVR and visible light blocks; however, this often renders them cosmetically unacceptable.

Recently, formulations containing nanoparticles of ZnO or TiO₂ have been developed. Micronising the particles improves the cosmetic appearance but reduces its photoprotection ability against visible light. When micronised, inorganic sunscreens have a similar mechanism to organic sunscreens, that is, absorption of UVR.

The UVA star rating system, developed in 1992 by Boots and Newcastle University, is a recognised system of determining sun protection against UVA. This is illustrated by the presence of one to five stars, symbolizing minimum to ultra‐protection, respectively.

An alternative symbol is UVA with an outer circle, which was established by The European Cosmetic and Perfumery Association (Colipa) It illustrates UVA protection in comparison to UVB in a product. A circle with UVA in the middle is permitted to be used on packaging if the UVA to UVB ratio is at least one third.

Similar to SPF ratings for UVB, persistent pigment darkening is a comparable rating system used for UVA. It measures the ratio of minimal dose of UVA required to induce pigmentation in protected to non‐protected skin. However, it is important to consider that persistent pigmentation can be produced by mechanisms other than melanogenesis triggered by UVR, such as oxidative stress.

Additionally, the protection grade of UVA (PA) system, developed in Japan, utilizes plus symbols to indicate the level of UVA protection a sunscreen offers. This ranges from PA+ to PA++++, with the latter indicating the highest level of UVA protection.

The SPF rating is based on the application of 2 mg/cm² of the product. This is approximately seven teaspoons per application and 33 ml of product for full body application. However, studies have shown that the general population only applies an average of 0.5 mg/cm², which means that the SPF on the label is not achieved. Furthermore, sunscreens with lower SPF ratings demonstrate a linear dose–response relationship, whereas with high SPF sunscreens, photoprotection decreases almost exponentially as the applied quantity decreases.

Sunscreens should therefore be applied generously to the skin and without gaps to ensure uniform coverage Most frequently missed areas include the neck, ears and temples. SPF determined using UVR solar simulators have also been shown to overestimate the SPF ability of sunscreens when used in natural sunlight, potentially due to a mismatch of spectral emissions.

Sunscreen should initially be applied 15–30 min before sun exposure and then reapplied 15–30 min after sun exposure has started, to increase the amount of the product on the skin. Two hourly reapplications are recommended and should be more frequent in the presence of vigorous activity or reapplied after swimming. In Europe and Australia, an expiration date is not a requirement on product labelling, but sunscreens should ideally be used within 3 years unless stated.

National Health Service in the United Kingdom advises applying a sunscreen with SPF 30 and UVA 4‐star protection rating or above, particularly during the months of March to October when the UV index is likely to be higher. The pillars of sun protection include avoidance of sunlight, seeking shade and covering skin with clothing. Sunscreens should be used as an additional measure in combination with these, rather than a solitary measure, and should not be used to extend the duration of sun exposure.

There are clear health implications that follow prolonged sunlight exposure and photoprotective measures, including sunscreen application, are required to reduce skin cancer risk and photoaging. Clinicians and patients must be aware of different types of sunscreens and their recommended application to achieve optimal benefits from use.

Exposure to UVR can be damaging; however, adverse effects due to sunscreen use has also been purported. Many UVR filters are relatively new, with their long‐term health and environmental effects unknown.

Not my own work. Taken from:

Salih H, Psomadakis C, George SMC. Sunscreens: A narrative review. Skin Health Dis. 2024 Aug 7;4(6):e432. doi: 10.1002/ski2.432. PMID: 39624735; PMCID: PMC11608887.

Copyright © 2026 by the authors.

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