Does Cotton Protect Against UV Rays?

Cotton can block some UV radiation, but ordinary cotton clothing should not automatically be considered sun protective. The amount of UV that passes through cotton depends on factors including fabric weight, weave, color, density, and construction.

In one study of cotton fabrics used for summer T-shirts, researchers found that two untreated white cotton fabrics had UPF values of just 4.94 and 3.13, providing limited protection from UV radiation. The researchers also found that dyeing and other fabric treatments could substantially increase UV protection.

That doesn't mean cotton is a poor summer fabric. It means “100% cotton” tells you very little about a garment's UV protection. Two cotton shirts can have dramatically different UPF values depending on how they're made.

Is cotton naturally UPF?

No. Cotton is a fiber, not a UPF rating. The finished fabric needs to be evaluated to determine how much UV radiation it blocks.

Research on textile UV protection consistently shows that fabric construction matters. Factors such as porosity, cover factor, thickness, color, and weave can substantially change a fabric's UPF.

Does dark cotton protect better than white cotton?

Generally, yes. Dyes can increase a fabric's ability to absorb UV radiation, meaning darker or more intensely colored fabrics can provide greater protection than comparable undyed or light-colored fabrics.

What should you look for instead?

If sun protection is the reason you're buying a garment, look for a tested UPF rating rather than relying on the fiber content. UPF 50+ indicates excellent UV protection, with no more than about 2% of UV radiation transmitted through the tested fabric.

The takeaway: cotton can provide some UV protection, but ordinary cotton clothing isn't necessarily sun protective. For reliable protection, choose clothing with a verified UPF rating.

Sources:
Sliney et al., Journal of the American Academy of Dermatology — “Reduction of ultraviolet transmission through cotton T-shirt fabrics…”
Gies et al., Cancer Research — “Clothing as protection from ultraviolet radiation: which fabric is most effective?”
Saha et al., Heliyon (2024) — “A comprehensive review of ultraviolet radiation and functionally modified textile fabric…”