What does UPF mean? Look for UPF, which stands for ultraviolet protection factor, on labels for clothing, hats, and fabrics. The number indicates what fraction of the sun’s UV rays can penetrate the fabric. A shirt labeled UPF 50, for example, allows just 1/50th of the UV radiation to reach your skin.
The pitfall: Any clothing leaves some skin exposed, so you need sunscreen, too. Don’t forget to apply it to your hands, especially after washing them. One of my favorite clothig resources for UV protective clothing is Coolibar