Sunscreens and Ultraviolet Light
Sunscreens and Ultraviolet Lightby Jasmine Chan
Source: “Sun Protection.” Soulage Wellness & Aesthetic Center, www.soulagemedspa.com/contents/our-products/sun-protection.
INTRODUCTION TO SUNSCREENS
Sunscreens, commonly known as sunblock is a substance which can absorb/reflect ultraviolet radiation (UV) from the sun on the skin which is exposed to sunlight. It can be in the form of a lotion, spray or gel which helps to protect against sunburns. [1] They work by absorbing UV light into heat. [2] Sunscreens help to reduce the risk of skin cancer, a dangerous type of cancer. They also help to reduce skin ageing, damage and sunburns. [3]
INTRODUCTION TO ULTRAVIOLET LIGHT
In order to understand how sunscreen works, the basics of UV light need to be understood. As ultraviolet light has shorter wavelengths than visible light, it means that it carries a lot more energy than visible light, meaning that it is able to cause photochemical damage to skin cells by damaging cellular DNA. [3,4]
There are 3 types of ultraviolet light: UVA, UVB and UVC. UVA and UVB are the harmful wavelengths whereas UVC does not cause any damage to the skin as it is absorbed by the ozone in the atmosphere before it reaches the surface of Earth. [3]
UVA has a wavelength of approximately 320-400nm which is responsible for 95% the UV light from the sun that reaches the Earth’s surface. UVA is able to penetrate deeply through the skin, into the connective tissue which causes pre-maturing and ageing of the skin, as well as wrinkling. This is because UVA destroys the structure of collagen, a protein in the skin. As the shape of collagen is altered due to UVA, wrinkles arise since the skin loses elasticity. [5] UVA is also able to generate reactive species in the skin which indirectly causes DNA damage which increases the risk of skin cancer.
UVB which has a wavelength of around 290-320nm is only responsible for 5% of the UV light reaching the Earth’s surface. Majority of UVB, like UVC, is absorbed in the atmosphere before reaching the Earth’s surface. In comparison to UVA, UVB does not penetrate as deeply into the skin, meaning that it is relatively less harmful to the skin. UVB causes the skin to produce more melanin and hence causes a person’s skin to appear darker. However, this causes direct damage to DNA, which increases the risk of skin cancer as well. [3]
The human skin contains molecules which are structured to absorb the energy of UVA and UVB wavelengths. This makes the molecule jump to a higher energy level as they become excited. When these molecules go back to the ground state, energy in the form of heat is released which causes molecules to undergo a chemical reaction. This energy released turns on the skin’s natural antioxidant network, which deactivates highly destructive reactive oxygen species (ROS) as well as free radicals, increasing the cellular damage in the skin. The ROS and free radicals formed are able to react with DNA which causes mutations to occur and hence leading to skin cancer. [5]
However, small amounts of UVA and UVB are important as they are used for the synthesis of vitamin D which helps to regulate the concentration of calcium and phosphate in the body which keeps bones and teeth healthy. [4,6] A lack of vitamin D can lead to rickets - a type of deformation in children, and osteomalacia - a type of bone pain in adults. [7]
TYPES OF SUNSCREEN
There are two types of sunscreen: physical sunscreen or chemical sunscreens. Physical sunscreens are able to reflect UV light whereas chemical sunscreens absorb UV light. [1] In most sunscreens nowadays, they contain both organic and inorganic compounds. [3]
Chemical sunscreens are usually organic, aromatic substances such as avobenzone, oxybenzone and octinoxate. [5,8] They are conjugated with a carbonyl (-C=O-) group. [1] Chemical sunscreens work by absorbing into the skin and then absorbing UV rays. These UV rays are then converted into heat and released from the body. [9] Some organic chemicals are photostable, whereas some are not, meaning that they would break down over time as the exposure to UV lights increases. Hence, sunscreen should be reapplied multiple times throughout the day. [3]
Physical sunscreens are commonly inorganic substances which sit on top of the skin after application and are able to reflect or scatter UV light. This includes chemicals such as zinc oxide and titanium dioxide.
Chemical sunscreens are easier to use than physical sunscreens as physical sunscreens tend to leave a white cast/residue on the face. However, physical sunscreens are hypoallergenic, which means that they are more suitable for sensitive skin as it reduces the irritation caused to the skin. [8] Physical sunscreens are also more moisturising on the skin as they are denser than chemical sunscreen. [6]
WHAT DOES SPF MEAN?
Sun protection factor, more commonly known as SPF, is a measurement used to measure the protectiveness of sunscreens against UVB. The SPF number is based on how long it takes for the skin to redden with and without the sunscreen. For example, if it takes 10 minutes for the skin to become red, an SPF 50 sunscreen would last 50 times longer, which is equivalent to around 8 hours (500 minutes). [8]
BIBLIOGRAPHY
[1] HariKishan, M.C.Sai, et al. “Sunscreen & Sunscreen Agents : A Review.” PharmaTutor, www.pharmatutor.org/articles/suncreen-agents-review.
[2] “The Difference between Physical and Chemical Sunscreen.” Piedmont Healthcare, www.piedmont.org/living-better/the-difference-between-physical-and-chemical-sunscreen.
[3] “The Science of Sunscreen & How It Protects Your Skin.” Compound Interest, 5 June 2014, www.compoundchem.com/2014/06/05/sunscreenchemicals/.
[4] Donev, Jason. “Ultraviolet Radiation.” Energy Education, 4 Jan. 2019, energyeducation.ca/encyclopedia/Ultraviolet_radiation.
[5] Wong, Michelle. “Chemical vs Physical Sunscreens: The Science (with Video).” Lab Muffin Beauty Science, 31 Mar. 2018, labmuffin.com/chemical-vs-physical-sunscreens-the-science-with-video/.
[6] “Sun Protection.” Soulage Wellness & Aesthetic Center, www.soulagemedspa.com/contents/our-products/sun-protection.
[7] “Vitamin D.” NHS, 3 Aug. 2020, www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/.
labmuffin.com/chemical-vs-physical-sunscreens-the-science-with-video/.
[8] Waxman, Eliana. “Feel the Burn? Explaining the Science of Sunscreen.” UChicago Medicine, UChicago Medicine, 18 July 2018, www.uchicagomedicine.org/forefront/health-and-wellness-articles/explaining-the-science-of-sunscreen.
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