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Biological Chemistry

Periodic Graphics

Periodic Graphics: The chemistry of how our skin responds to the sun

Chemical educator and Compound Interest blogger Andy Brunning illuminates the biochemistry behind sunlight’s effects on our skin.

by Andy Brunning, special to C&EN
July 18, 2021 | A version of this story appeared in Volume 99, Issue 26


The first column of the infographic explains that ultraviolet radiation is emitted by the sun along with visible light. Exposure to UV is what causes skin to tan and burn. UVC light is absorbed by the atmosphere, but longer-wavelength UVB and UVA light can penetrate the skin and damage DNA. This damage can ultimately lead to skin cancer, but some exposure to UV light is important for our skin to make vitamin D.

The second column of the infographic explains that when our skin is exposed to UV light, melanocytes, cells in the skin's epidermis, produce melanin. Melanin is a protective, polymeric pigment that absorbs UV radiation and dissipates it as heat. Increased melanin is what gives the appearance of darker skin in some people.

UV radiation can directly damage DNA. It causes reactions between DNA bases, and these reactions form products including pyrimidine dimers, the primary cause of skin cancer in humans. DNA can also be damaged indirectly by reactive oxygen species generated when excited melanin generates reactive oxygen species.

DNA-repair enzymes repair damaged DNA in cells by removing and correcting defective sections. But if cells become too damaged, they self-destruct and send a signal to immune cells. This signal causes increased blood flow and inflammation, giving the characteristic pain (and sometimes redness) of sunburn.

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References used to create this graphic:

Clancy, Suzanne. “DNA Damage & Repair: Mechanisms for Maintaining DNA Integrity.” Nat. Educ. (2008).

De Gruijl, Frank R., Henk J. van Kranen, and Leon H. F. Mullenders. “UV-Induced DNA Damage, Repair, Mutations and Oncogenic Pathways in Skin Cancer.” J. Photochem. Photobiol., B (Oct. 2001). DOI: 10.1016/S1011-1344(01)00199-3.

Hopkins, Ryan. “How Ultraviolet Light Reacts in Cells.” SciBytes (blog). Feb. 14, 2015.

Soyer, H. Peter, and Katie Lee. “Explainer: What Happens to Your Skin When You Get Sunburnt?” Conversation, March 9, 2016.

A collaboration between C&EN and Andy Brunning, author of the popular graphics blog Compound Interest

To see more of Brunning’s work, go to To see all of C&EN’s Periodic Graphics, visit



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