Protecting yourself from the sun is crucial, especially in summer when the UV ratings each day are higher. But wearing sunscreen works only so well if you're sweating constantly; even water-resistant sunscreen can sweat off after a time. Covering up with protective clothing, like long-sleeve tees, can help protect you without requiring you to stop and slather on extra sunscreen that will soak into your clothes instead of staying on your skin.
Ultraviolet Protection Factor
The most important feature to look for is an ultraviolet protection factor number or UPF. Many sports and outdoor clothing now comes with a sunscreen baked right into the clothing fabric; some brands create a special weave that provides the UPF rather than resorting to chemical usage. UPF clothing functions like sunscreen except it doesn't fade when you start to sweat.
Slightly Longer Sleeves
The sleeves on the shirt should not interfere with your hands or wrists. However, it can be valuable to have slightly longer sleeves just so that you get a little extra coverage on the wrist. This is helpful when you have to wear sports-related gloves that don't cover the wrist at all. You can also use the extra material to shade your hands when you're taking a break.
Ventilation, Not Cut-Outs
Performance tees need to breathe, whether they have a UPF factor or not. Look for ventilation panels, such as in the armpit areas, that allow you to cool off. If the shirt does not allow for good ventilation, you'll overheat more easily. Do not substitute cut-outs for ventilation. If you find performance tees (this is especially true for women's clothing) that have ornamental cut-outs on the back, arms, and elsewhere, look for another shirt. Those cut-outs aren't going to provide any protection. And, if the sun shines directly on them, they really aren't going to provide adequate ventilation.
Hoods or Collars
Most tees will have crewnecks, but a few styles have attached hoods or collars. These help protect the back of your neck. You could always wear a hat with fabric flaps in the back, but sometimes a shirt with an attached hood is most convenient. There's less risk of you losing the hood as you take part in a sport.
If you can, you should wear sunscreen. But having to reapply sunscreen to the skin under your shirt constantly can be annoying and time-consuming. It's much easier to wear clothing that offers sun protection. For more information on long sleeve performance tees, contact your local athletics apparel store.