The answer to whether you can tan or burn through a white shirt is a definitive yes, because the sun’s radiation easily passes through many common textiles. Tanning and sunburn occur when the skin is exposed to ultraviolet (UV) radiation from the sun, categorized into UVA and UVB rays. UVA radiation penetrates deeply, causing existing melanin to darken, while UVB rays trigger new melanin production, leading to delayed tanning and sunburn. A typical, lightweight white shirt provides far less protection than most people assume, allowing a significant amount of these damaging rays to reach the skin.
How UV Radiation Penetrates Fabric
UV radiation manages to bypass a layer of clothing through two primary physical mechanisms. The first is the penetration of light through the microscopic gaps present in the fabric’s weave or knit structure. Standard clothing is not a solid, uniform barrier, but rather a network of fibers with tiny pores that allow UV photons to pass directly through to the skin beneath.
The second mechanism involves the transmission of UV light directly through the fibers themselves, influenced by the fiber’s material composition and thickness. While fabric fibers absorb some radiation, they cannot block all of it, especially if the fibers are thin or lack inherent UV-absorbing properties. The overall protection level of any garment is a combined result of how tightly the threads are packed and the material’s ability to absorb or scatter the light.
Understanding the Ultraviolet Protection Factor (UPF)
To provide consumers with a reliable measure of sun protection from clothing, the industry uses the Ultraviolet Protection Factor (UPF) rating. This rating indicates how effectively a fabric blocks both UVA and UVB radiation from reaching the skin. Unlike the Sun Protection Factor (SPF) for sunscreen, the UPF rating applies specifically to textiles.
The UPF value is determined by laboratory testing and translates directly to the fraction of UV radiation that can pass through the material. For example, a garment with a UPF of 30 allows only 3.3% (1/30th) of the sun’s UV rays to penetrate the fabric.
The UPF scale uses three categories: minimum protection (UPF 15 to 24), good protection (UPF 25 to 39), and excellent protection (UPF 40 to 50+). A rating of UPF 50+ means the fabric blocks at least 98% of the sun’s UV radiation, offering the highest level of reliable coverage. Consumers seeking dependable sun protection should look for garments that explicitly carry a UPF rating on the label.
Why Color and Fabric Matter More Than You Think
The protective quality of a shirt is highly dependent on its physical characteristics, explaining why a simple white T-shirt offers minimal defense. A typical white cotton T-shirt, especially when light and loosely woven, may have a UPF rating as low as 5, allowing about 20% of UV radiation to pass through. Weave tightness is a primary determinant of protection, as a denser knit minimizes the size of the holes that allow direct UV penetration.
Darker colors, such as black, navy, or deep red, offer superior protection compared to light colors like white or pale pastels. This is because dark dyes contain compounds that act as effective UV absorbers, preventing the radiation from reaching the skin. While white fabric reflects visible light, it generally transmits more UV radiation unless chemically treated to enhance its protective capacity.
The material composition also plays a large role in the fabric’s natural ability to block UV rays. Synthetic fibers like polyester and nylon are more protective than untreated natural fibers like cotton because their chemical structure and density absorb UV light more effectively. The condition of the garment significantly alters its level of protection, as wetness drastically reduces the UPF value by decreasing the light scattering effect. Stretching the fabric, which occurs with a tight fit or during movement, also lowers the protection by pulling the weave apart and enlarging the pores.