At one time, the only people who wore compression socks were those with blood flow problems or swelling in their legs. Not anymore. Those are still common reasons to wear the socks. But, in recent years, their popularity has expanded. For instance, many runners and other athletes now wear them, hoping to improve their performance. What a runner needs in compression socks is probably not the same as someone who needs them for swelling. Different types of socks do different things. Here's how to figure out what would be best for you. Socks for Athletes and Runners Compression socks for athletes are now so popular you can find styles labeled “running compression socks.” There are men's and women's sizes. They come in a variety of patterns and colors. These socks usually have a low level of compression. They would not be good for medical treatment. Whether they truly do improve performance still hasn't been proven. Still, many athletes like them. And, wearing them appears to cause no harm. Prescription Socks Doctors sometimes prescribe compression socks for people with circulation problems. This includes people who've had deep vein thrombosis (DVT)—a clot in a vein deep in your body, often in a leg. Sometimes people who've had DVT still have pain, swelling, or other symptoms after the clot is gone. This is post-thrombotic syndrome (PTS). People with PTS also might benefit from wearing compression socks. So might people with other serious circulation problems in their legs. If you need these socks, your doctor will prescribe compression socks that apply a specific amount of pressure—called compression strength—to your leg. A medical professional at your pharmacy or a medical supply store can measure your leg and custom-fit a stocking that meets your doctor's prescription. The compression strength is given in millimeters of mercury (mmHg). The greater the number, the higher the pressure. These socks carry a classification number—a Roman numeral. The number indicates the amount of pressure they apply. The pressure at the ankle determines the grade of the sock. For example, a Class I sock applies 20 to 30 mmHg of pressure at the ankle. A Class IV sock applies 50 to 60 mmHg. Most socks apply less pressure as they progress up the leg. The class of compression sock that is best for you depends on your size, your age, and the medical condition the socks will help treat. That's why it’s important to get a prescription from your doctor rather than choosing socks on your own. As an example, people trying to prevent or treat PTS often need socks that apply 30 to 40 mmHg of pressure. However, people who have leg swelling will probably need more pressure, based on how much swelling there is. TED Stockings Another type of compression sock is a TED stocking. That stands for thrombo-embolic deterrent. These socks apply less pressure than most prescription stockings. Doctors might recommend them for people who've just had surgery. Or, they might suggest them for people who are on bed rest and can’t move around much. The lower pressure of the stockings promotes good circulation. This helps prevent clots while you're immobile. These socks don't have enough pressure to treat problems such as DVT in someone who's active. Stocking Length Compression socks come in various lengths. Full-length socks cover the entire leg. Some go thigh high. Others are knee length. Pantyhose, tights and leotards that apply compression are available, too. People usually say the knee-length socks are the most comfortable and easiest to put on. But, follow your doctor’s recommendation to make sure you get the socks that will best help your condition.