How Sunscreen Protects your DNA: The Science Behind SPF

Raneen Awada
Sep 15
3 min read

We often think of sunscreen as a way to prevent sunburn, however, its function goes beyond just surface level. Sunscreen protects the DNA in skin cells from harmful ultraviolet (UV) radiation, helping prevent skin cancer, premature aging, and immune system suppression. By understanding the science behind sunscreen, smarter choices can be made about daily skin protection.

UV Radiation and DNA Damage

The sun emits two major types of UV rays that affect the skin: UVA and UVB

UVB rays (shorter wavelength) damage the outer layers of the skin and directly harm the DNA by forming pyrimidine dimers, which can trigger mutations. This is the cause of sunburn.
UVA rays (longer wavelength) penetrate deeper into the skin. They don't burn as quickly, but they cause indirect DNA damage by generating reactive oxygen species, which are unstable molecules that harm skin cell structures, including DNA and proteins.

According to Harvard Health and UChicago Medicine, both UVA and UVB contribute to skin aging, immune suppression, and forms of skin cancer, including deadly melanoma. UVA. in particular, is often overlooked because it doesn't cause visible burns. but it accounts for over 90% of UV exposure and is present all day, year-round.

How Sunscreen Shields the Skin

Sunscreens act as protection for the skin by using chemical and physical filters to block or absorb harmful UV rays before they can reach and damage skin cells.

Chemical filters (like avobenzone or oxybenzone) absorb UV radiation and transform it into heat.
Physical (mineral) filters (like zinc oxide and titanium dioxide) reflect and scatter UV rays off the skin's surface.

Broad-spectrum sunscreens combine both types to provide protection against both UVA and UVB. This is crucial because a sunscreen that only protects against UVB may prevent sunburns, but still allow deep UVA damage that harms the DNA.

What does SPF mean?

SPF, or Sun Protection Factor, refers to how well a sunscreen protects against UVB radiation.

SPF 30 blocks around 97% of UVB rays, while SPF 50 blocks about 98%.
High SPF sunscreens still must be applied correctly and reapplied every 2 hours, especially after swimming or sweating. Most people apply far less than the recommended amount, which significantly lowers protection.

Dermatologists recommend about 1 ounce for full body coverage and a nickel-sized amount or two fingers-length amount for the face. Sunscreen should be applied 15-30 minutes before sun exposure.

UV radiation damages skin cells every time someone is in the sun, even when it's cloudy or cool outside. This damage accumulates over time. According to UChicago Medicine and Harvard Health, regular sunscreen use significantly reduces the risk of squamous cell carcinoma, basal cell carcinoma, and melanoma. It also prevents signs of aging such as wrinkles sunspots and skin thinning.

DNA damage in skin cells not only increases cancer risk, but also weakens the skin's ability to repair itself and fight infections. Protecting DNA protects long-term health.

Sunscreen is scientifically proven to protect the skin on a microscopic level. By using a broad-spectrum SPF, applying it generously and regularly, and pairing it with sun-safe habits (such as hats and sunglasses), smarter steps are being taken to shield DNA from the sun's silent, but lasting effects.

Gabros, Sarah, et al. “Sunscreens and Photoprotection.” StatPearls, Mar. 2025.

de Luzuriaga, MD, MPH, MBA, Arlene Ruiz, and Oluwakemi Onajin. “Feel the Burn? Explaining the Science of Sunscreen.” UChicago Medicine, https://www.uchicagomedicine.org/forefront/health-and-wellness-articles/explaining-the-science-of-sunscreen. Accessed 24 July 2025.

“The Science of Sunscreen.” Harvard Health, 1 July 2018, https://www.health.harvard.edu/staying-healthy/the-science-of-sunscreen. Accessed 24 July 2025.

Assessed and Endorsed by the MedReport Medical Review Board