In the realm of skincare, there’s no more influential factor than Sunlight. It’s a source of warmth, light, and vitality, but it also harbors potential dangers if not respected. While most of us know the basics of sunlight exposure and its effects on our skin, looking deeper reveals an interplay of biology, chemistry, and physics. Understanding the direct impacts Sunlight has on our skin is not just about avoiding sunburn; it’s about safeguarding our skin’s health for the long term.
I was struggling with severe acne during my teenage years. Well into my thirties I had mild acne. No remedies really helped until I started using sunscreen daily to protect my skin and give it the needed space to heal.
The effects Sunlight has on us and our skin will be described in detail in the following chapters. All information is backed up by scientific research and studies with the source material stated accordingly: (source author. year of publication).
The Science of Sunlight
The Sun produces most of its radiation as energy through nuclear fusion reactions and emits light in virtually every part of the electromagnetic spectrum.
According to NASA: ‘The electromagnetic spectrum describes all of the kinds of light, including those ours eye cannot see. In fact, most of the light in the universe is invisible to us. The light we can see, made up of the individual colors of the rainbow, represents only a very small portion of the electromagnetic spectrum. Other types of light include radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays and gamma rays (Figure 1) — all of which are imperceptible to human eyes.’
Sunlight reaching the Earth’s surface
So, which portions of the electromagnetic spectrum should we be concerned about?
Earth has a natural sunscreen in the atmosphere: a layer of ozone gas in the stratosphere which envelopes our planet. It acts like a shield, preventing much of the Sun’s harmful radiation from reaching Earth’s surface and our skin.
As shown above in Figure 2, only a small portion of radiation, primarily Visible Light, some Infrared (IR), Ultraviolet (UV) light and Radio waves, reaches the Earth’s surface due to our atmosphere filtering out much of the other more harmful radiation.
- Ultraviolet radiation (wavelengths between 100–400 nm) comprises around 5% of solar radiation reaching Earth’s surface. (E. Austin et al., 2021).
- Infrared (wavelengths between 700 nm-1 mm) comprises 45% of solar radiation that reaches Earth’s surface. (E. Austin et al., 2021)
- Visible Light (between 400–700 nm) is electromagnetic radiation that our eye can detect. Around 50% of the solar radiation reaching Earth’s surface is Visible Light, which can be divided based on color and wavelength (Figure 5). (E. Austin et al., 2021)
- The Radio waves from the Sun that reach the Earth are relatively weak and are not harmful to human health. They are part of the natural background radiation that we are exposed to every day.
Sunlight Effects on Skin by: Ultraviolet Radiation
Human exposure to sunlight and its UV radiation has both beneficial and harmful effects on us and our skin (Juzeniene et al., 2011; Lucas et al., 2006).
While ultraviolet radiation from the Sun is the best natural source of vitamin D, it is also one of the major causes of skin cancer, despite it being one of the most preventable types of cancers. In 2020, doctors diagnosed over 1.5 million cases of skin cancer (melanoma and non-melanoma combined) globally. Additionally, the Sun’s ultraviolet rays can cause DNA damage and certain eye diseases, such as cataracts (European Commission and Copernicus).
Apart of skin cancer, other harmful effects from overexposure to UV radiation are:
- Erythema (skin reddening)
- Eye diseases (snow blindness, cataracts)
- Photoaging (premature aging of the skin due to light exposure)
- Suppression of the body’s immune system (European Commission Recommendation, 2006).
The Sun emits three types of UV rays:
UVA
According to Fu & Lu, ‘The longest of the three wavelengths, UVA makes up 95% of the UV that reaches our skin. UVA can reach all the way down to the dermis (shown in Figure 3) and is responsible for deep photoaging and enhanced skin cancer development.’
UVB
As shown on Figure 3, UVB rays mostly penetrate the upper skin layer (epidermis) (Fu & Lu, 2021). UVB primarily causes skin reddening, sunburn and, eventually, skin cancer.
A significant beneficial effect of exposure to solar UVB radiation is the synthesis of Vitamin D in our skin (Holick, 2002; Webb et al., 2020; Webb et al., 2011). If you want to know more about how to protect yourself from the harmful effects of UVB radiation and at the same time get enough vitamin D, please read my Vitamin D post.
Another benefit of UVB is its common use in psoriasis treatments (E. Austin et al. in 2021).
UVC
UVC is the shortest of the three UV wavelengths. Luckily, the ozone and oxygen molecules absorb UVC as Sunlight passes through the atmosphere (World Health Organisation, 2016).
Otherwise, UVC is so powerful that it is able to kill unicellular organisms on exposure. Depletion of the ozone layer has been a matter of concern since the 70s. At the time, a series of publications showed that certain inert gases, such as chlorofluorocarbons (CFCs), released in the atmosphere by human activities could affect the ozone layer. This culminated in 1985 with the report of a growing hole in the ozone layer over Antarctica. In reaction, the Montreal Protocol was adopted in 1987 leading to a global ban on CFC production. Ozone kept declining until 1995, but has been slowly recovering since then. This is good news for the future; however, there is another threat to the ozone layer on the horizon, in the form of greenhouse gases and climate change. (E. Dupont et al., 2012)
The ozone absorbs UVC (99%), some UVB (90%), but little to no UVA or Visible Light (50%).
We can monitor the Ozone layer using the Copernicus Atmosphere Monitoring Service (Figure 4).
Sunlight Effects on Skin by: Infrared Radiation
We encounter Infrared radiation every day; we cannot see it, but we can detect it as heat i.e. thermal energy (NASA).
Negative effects from exposure to infrared radiation such as thermal burns, photocarcinogenesis (the development of cancer due to exposure to light), and photoaging have been reported by scientific evidence, but these are mostly the result of the heat generated by the infrared radiation rather than from the radiation itself. (L. Horton et al., 2023)
Studies that aim to reproduce these negative effects of infrared radiation in the laboratory use infrared light irradiances (optical power received by a surface per unit area) far beyond what humans are exposed to in nature. This suggests that the adverse effects observed in these studies may not accurately reflect the risks associated with normal exposure to infrared radiation in everyday life. Therefore, some experts argue that protection against this isolated waveband has no proven benefit. (L. Horton et al., 2023).
Although there is no filter that specifically blocks infrared radiation, the addition of antioxidants in sunscreen formulations may offer some protection. (L. Horton et al., 2023)
Infrared radiation may have some beneficial properties when administered in controlled doses and conditions using infrared light emitting devices in doctor’s facilities (L. Horton et al., 2023). If you are interested in a more in depth analysis of the benefits of infrared light, have a look at this post.
Sunlight Effects on Skin by: Visible Light
Visible Light can be classified into 4 categories, according to the wavelength and color. These are blue light, green light, yellow light and red light, with the wavelength of 400–490 nm, 490–570 nm, 570–595 nm, and 630–770 nm, respectively. Furthermore, the longer the wavelength, the deeper the Visible Light can penetrate into the skin. Therefore, red light can penetrate through the full thickness of the epidermis and dermis, while blue light has less penetration (Figure 5). (He X et al., 2023)
Up until recently, Visible Light was thought to not have a significant effect on the skin. However, updated research suggests that this is not the case and measurable effects of Visible Light on the skin are documented for all skin types. (Sh. Narla et al., 2020)
Visible Light has been reported to cause:
- Erythema (redness of the skin) in light skin (Henry W. Lim et al., 2022), also in combination with UVA radiation exposure.
- Pigmentary changes in skin of color (Henry W. Lim et al., 2022), which can be more intense and sustained than UVA induced pigmentation (N. Ezekwe et al., 2022, E. Austin et al., 2021). Pigmentary changes were also seen in tissue samples extracted from light skin after multiple exposures to Visible Light (M. Randhawa et al., 2015).
Therefore, you should protect ourselves from Visible Light.
If you want to know more about how sunscreen can protect you against the negative effects of Visible Light and which ingredients it should contain to do so, read the post Get to know your sunscreen.
Visible Light therapy is commonly used for various skin diseases in dermatologist offices and at home. I summerised the benefits of Visible Light and Visible Light emitting devices in this post.
References
A-E
Dupont E, Gomez J, Bilodeau D. Beyond UV radiation: a skin under challenge. 2013. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/23406155/
E. Austin, A. N. Geisler, J. Nguyen, I. Kohli, I. Hamzavi, H. W. Lim and J. Jagdeo. Visible Light Part I. Properties and Cutaneous Effects of Visible Light.
F-J
Fu, V., & Lu, G. (2021). Skincare Decoded. Publisher Weldon Owen.
Holick, M. F.: Vitamin D: the underappreciated D-lightful hormone that is important for skeletal and cellular health, Current Opinion in Endocrinology, Diabetes and Obesity, 9, 2002. Retrieved from: https://www.researchgate.net/publication/232218729_Vitamin_D_The_underappreciated_D-lightful_hormone_that_is_important_for_skeletal_and_cellular_health
H. W. Lim, I. Kohli, E. Ruvolo, L. Kolbe, I. H. Hamzavi (March 2022). Impact of visible light on skin health: The role of antioxidants and free radical quenchers in skin protection. Retrieved from: https://www.sciencedirect.com/science/article/abs/pii/S0190962221029893
He X, Jin S, Dai X, Chen L, Xiang L, Zhang C. The Emerging Role of Visible Light in Melanocyte Biology and Skin Pigmentary Disorders: Friend or Foe? 2023. Retrieved from: https://www.mdpi.com/2077-0383/12/23/7488
Juzeniene, A., Brekke, P., Dahlback, A., Andersson-Engels, S., Reichrath, J., Moan, K., Holick, M. F., Grant, W. B., and Moan, J.: Solar radiation and human health. 2011. Retrieved from: https://lup.lub.lu.se/search/ws/files/3790568/2370319.pdf
K-O
Lucas, R., McMichael, T., Smith, W., Armstrong, B. K., Prüss-Üstün, A., and World Health, O.: Solar ultraviolet radiation : global burden of disease from solar ultraviolet radiation / Robyn Lucas … [et al.] ; editors, Annette Prüss-Üstün … [et al.]. Environmental burden of disease series ; no. 13, World Health Organization, Geneva, 2006.
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M. Randhawa, I. Seo, F. Liebel, M. D. Southall, N. Kollias, E. Ruvolo (29 June 2015). Visible Light Induces Melanogenesis in Human Skin through a Photoadaptive Response. Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4488093/
NASA (September 30, 2022). The Electromagnetic Spectrum Article. Hubblesite. Retrieved from https://hubblesite.org/contents/articles/the-electromagnetic-spectrum
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U-Z
Webb AR, Engelsen O. Ultraviolet Exposure Scenarios: Balancing Risks of Erythema and Benefits of Cutaneous Vitamin D Synthesis. 2020. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/32918230/
Webb, A. R., Slaper, H., Koepke, P., and Schmalwieser, A. W.: Know Your Standard: Clarifying the CIE Erythema Action Spectrum. 2011. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/21366601/
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World Health Organisation (20 June, 2022). Radiation: The ultraviolet (UV) index. Retrieved from https://www.who.int/news-room/questions-and-answers/item/radiation-the-ultraviolet-(uv)-index