Introduction:
In different parts of the world, people have adopted various practices to protect their skin from harmful UV rays. In ancient Egypt a thick coat of rice bran paste was applied, while olive oil was used by the ancient Greeks. Then, “in 1932”, sunscreen as we know it today was introduced for the first time (1). Intrigued? Dive deeper if you want to uncover the fascinating science behind the sunscreen we use today.
Sunscreens help to protect the skin from harmful effects of UV radiation by absorbing, reflecting, scattering, or deflecting UV protons. This helps to avoid their absorption by the components of the skin (2).
The SPF value, also known as the Sun Protection Factor Value, is something we often look at before purchasing a sunscreen. But what exactly does it mean? SPF is the ratio of energy needed to produce a minimal erythema dose through the sunscreen compared with the energy required to produce the same reaction in the absence of sunscreen.(2). In simpler terms, it tells us how well the product protects us from getting a sunburn. However, a higher SPF value does not mean double protection.
UVA and UVB are the two types of UV rays. Each ray penetrates the skin differently. The SPF factor only refers to the UVB rays (3). In an experimental setting, sunscreen was evenly applied to the skin and then exposed to controlled lighting. A sunscreen of SPF 15 blocked 93% of UVB radiation, and SPF 30 blocked 97%. SPF 50 blocked 98%, and SPF 100 blocked 99% of the UVB rays from penetrating the skin. (3) UVA rays are present in much higher sunlight levels and are a major cause of wrinkles, freckles and sun spots. Therefore, choosing a broad-spectrum sunscreen is key as it protects from both UVA and UVB rays (3).
Fig1: the difference when UV rays hit the unprotected skin versus when a broad spectrum sunscreen is applied (7).
However, what exactly would be the right sunscreen? The American Academy of Dermatology recommends finding a sunscreen that has a SPF 30+, broad spectrum, and is water resistant (6). Moreover, there are two types of sunscreen: Mineral and Chemical - which function quite differently.
Mineral sunscreens reflect the UV rays of the sun. A barrier is created by the active ingredients titanium dioxide and zinc oxide. This barrier reflects UV light. According to dermatologist Dr. Anisha Patel: “Mineral sunscreens offer the most protection because they’re creating a physical separation between you and the sun”. Mineral sunscreens should be reapplied every two hours, especially if we sweat or swim (4).
Chemical sunscreens change their chemical structure to absorb UV rays helping reduce sun damage. Most chemical sunscreens contain a few of the active ingredients. In the United States these typically include aminobenzoic acid, avobenzone, octisalate, octocrylene, and oxybenzone (5). Chemical sunscreens should be re-applied more often and are available in spray and cream forms. Spray sunscreens are convenient, but it is crucial not to miss a spot (4). Hybrid sunscreens offer the best of both. They offer better protection from mineral sunscreen but have a thinner formula. This helps to blend them better. (4)
Fig 2: The difference in how mineral sunscreen and chemical sunscreen works (8)
Next, lets dive deeper into the chemicals present in sunscreen. We may often come across people or articles arguing that sunscreens are harmful to us. In chemical sunscreens, one of the active ingredients is Oxybenzone which has been criticized the most for being known as a hormone disruptor. A hormone disruptor is a chemical with an ability to cross cell membranes and interfere with the body’s natural hormone production (5). However, there has been no conclusive evidence of oxybenzone being harmful. Skin cancer is one of the most common cancers in the United States and using sunscreen is one of the ways to protect oneself (6).
Lastly, some safety tips to follow to prevent sun damadge. Firstly, try to avoid or reduce sun exposure rather than using just sunscreen (5). Nowadays, using sun-protective clothing is becoming more popular. Sun-protective clothing can either be chemically treated or woven with slightly tighter woven material to block the sun (4). However, it is key to read the labels, and replace them when necessary because the chemical protection wears off over time (4). Seek shade and avoid tanning beds (6). Finally, reapply, reapply and reapply. The effect of sunscreen wears off even quicker when we sweat or swim. Chemical sunscreen should be reapplied every 2 hours, which is more frequent than mineral sunscreens (5).
Bibliography:
Team, B.O.B. and Wetsel, A. (2022) When was sunscreen invented – the history of Sunscreen, WHEN WAS SUNSCREEN INVENTED – THE HISTORY OF SUNSCREEN. Available at: https://brushonblock.com/blogs/news/sunscreen-who-invented-sunscreen (Accessed: 12 August 2023).
Philips , N. et al. (2021) Fern extract, oxidative stress, and skin cancer, Cancer (Second Edition). Available at: https://www.sciencedirect.com/science/article/abs/pii/B9780128195475000341#ab0010 (Accessed: 10 August 2023).
Alexander, H. (2021) Should you use very high SPF sunscreen?, MD Anderson Cancer Center. Available at: https://www.mdanderson.org/cancerwise/should-you-use-very-high-spf-sunscreen.h00-159460845.html (Accessed: 15 September 2023).
Adams, M. (2022) Mineral or chemical sunscreen: Which should you choose?, MD Anderson Cancer Center. Available at: https://www.mdanderson.org/cancerwise/is-mineral-sunscreen-better-than-chemical-sunscreen.h00-159540534.html (Accessed: 16 September 2023).
The Science of Sunscreen (2021) Harvard Health. Available at: https://www.health.harvard.edu/staying-healthy/the-science-of-sunscreen (Accessed: 12 September 2023).
White, T. (2022) Sunscreen, explained, Healthline. Available at: https://www.healthline.com/health/sunscreen-explained#finding-the-right-sunscreen (Accessed: 16 September 2023).
Hlushko, M. (2021) UV penetration into the layers of the skin. infographic of sunscreen protection against UVA, UVB rays. skin anatomy stock vector - illustration of melanoma, epidermis: 221005928, Dreamstime. Available at: https://www.dreamstime.com/uv-penetration-layers-skin-infographic-sunscreen-protection-against-uva-uvb-rays-skin-anatomy-broad-spectrum-image221005928 (Accessed: 15 September 2023).
Savay, A. (2020) Differences between chemical and mineral sunscreens, Harken Derm. Available at: https://www.harkenderm.com/blog/2018/8/16/the-difference-between-chemical-and-mineral-filters (Accessed: 16 September 2023).