Clothes can protect your skin against the sun's harmful ultraviolet (UV) rays. But not all clothing is created equal. How the clothes are made, the dyes used and whether or not the material is treated with additives all affect the amount of protection they provide.
As a rule, light-colored, lightweight and loosely-woven fabrics do not offer much protection from the sun. That white T-shirt you slip on at the beach when you feel your skin burning provides only moderate protection from sunburn, with an average sun protection factor (SPF) of 7. At the other end of the spectrum, a long-sleeved dark denim shirt offers an estimated SPF of 1,700 – which amounts to a complete sun block. In general, clothing made of tightly-woven fabric best protects skin from the sun. The easiest way to test if a fabric can protect your skin is to hold it up to the light. If you can see through it, then UV radiation can penetrate it – and your skin.
The color of the fabric also plays a role. Darker-colored fabrics are more effective than lighter at blocking out the sun. For instance, the SPF of a green cotton T-shirt is 10 versus 7 for white cotton, and a thicker fabric such as velvet in black, blue or dark green has an approximate SPF of 50.
What the clothing is made of matters. Fabrics such as unbleached cotton contain special pigments called lignins that act as UV absorbers. High-luster polyesters and even thin, satiny silk can be highly protective because they reflect radiation.
Even if the piece of clothing has a good SPF, what you do while wearing it can make a difference. If the fabric gets stretched, it will lose some of its protective ability, because the fabric becomes thinner and more transparent to light. And once it gets wet, it can lose up to 50 percent of its SPF. In Florida, it is a common practice for parents to put a white T-shirt on their children to protect them from the sun while swimming. But when that T-shirt gets wet, it provides an SPF of only 3.
High-Tech Clothing and UPF
When selecting clothes for sun protection, consider fabrics that have been specially treated with UV absorbers. Many companies offer high Ultraviolet Protection Factor (UPF) clothing which incorporates colorless compounds to shield those parts of the body most likely to be overexposed to the sun.
It is important to understand the labeling information on sun-protective clothing. New standards for sun-protective fabrics in the US were unveiled in January, 2001. UPF is similar to SPF, in that they both measure sunburn protection. But UPF ratings measure how much of both ultraviolet B (UVB) and ultraviolet A (UVA) radiation is blocked, whereas SPF is a measurement of UVB protection only. This can be critical for people who have had skin cancer or are undergoing radiation or chemotherapy.
The UPF rating indicates how much of the sun's UV radiation is absorbed. A fabric with a rating of 50 will allow only 1/50th of the sun's UV rays to pass through. This means the fabric will reduce your skin's UV radiation exposure significantly, because only 2 percent of the UV rays will get through.
Only clothes with a UPF of 15-50+ may be labeled as sun-protective. Also, like regular clothing, sun-protective clothing may lose its effectiveness if pulled too tight or stretched out, if it becomes damp or wet, or if it is washed and worn repeatedly.
Laundry additives can substantially increase a fabric's SPF. When washing your clothes, add specialized laundry detergents that contain sun-protective ingredients. The treated fabric will remain UV-protective for approximately 20 washings.