You've just done a half hour on the StairMaster and kickboxed your way to a tighter set of glutes—now all you want to do is hit the sauna and relax. According to exercise physiologist Neil Sol, Ph.D. (affiliated with the American College of Sports Medicine), you may want to head straight for the shower instead. "At the end of the day," says Sol, "It's probably not good to use a sauna, steamroom, or whirlpool after exercise." 

Why? "When you exercise, it's natural for your body temperature to rise a couple of degrees—maybe to one hundred, depending on individual efficiency and other factors—but, in the majority of cases, it will still be lower than the temperature of the atmosphere in a sauna, steam room, or whirlpool," says Sol. (A sauna needs to be about 170°F to 180°F and up to 5 percent humidity; a steam room is generally 100°F to 110°F, 100 percent humidity; a whirlpool's temperature is about 102°F to 104°F.) "These facilities present an external heat load. And since heat naturally moves from a higher temperature to a lower temperature, they don't give your body the chance to cool down."

If you work out and then sit in a steam room, for example, steam will flow into your body and not leave it. The same is true of a whirlpool or sauna—they bring heat to you and don't let it escape. Your body is forced to work harder when it cannot dissipate heat. "Your heart has to pump harder and blood pressure must rise, in order to send blood to the surface of the skin to try to keep your core body temperature cool," explains Sol. "The key here is that your body's efforts to cool itself are futile in these hot environments because your body temperature will always be less than these facilities and the heat will continue to enter, not exit, your body. This process can create a heat stress that results in heat exhaustion or heat stroke, and can be very harmful." It is worth noting, however, that everyone does not acclimate equally, and all people are not subjected to the same risks when exposed to extreme heat. To be sure, you should be in tune with how you react and feel in these hot environments.

"Physiologically," says Sol, "these kinds of equipment are not necessary." While Sol agrees that perspiring can rid your body of impurities, he believes that exercise—certainly not sitting in a room hotter than your natural body temperature—is the best way to release toxins. And, while there are some who advocate the use of saunas, steam rooms or whirlpools as warm-ups to elasticize your muscles, Sol still maintains that artificially heating your body is not the best option. So, why are they so popular and readily used? Whirlpools can be soothing in the case of sore muscles, joints, or limbs because they can increase blood flow to that area, thereby promoting healing. "The problem, even in this instance, is that you subject the rest of your body to the heat stress by submerging it in the 100-plus-degree water—so there is a tradeoff," says Sol. The most obvious and widespread rationale for using these facilities is that they feel good. For some, whirlpools, saunas, and steam rooms feel stress-reducing and relaxing. In which case, Sol says, "Trust your body and your instincts—use these facilities if you genuinely feel great doing so, not because you think they are good for you."

Before you head for the sauna, steamroom, or whirlpool, Sol recommends keeping these tips in mind:

1. Do not go over a 10-minute limit; your body temperature will get too high.

2. Avoid them if you have difficulty breathing, like asthmatics, or cardiac or pulmonary patients. 

3. Check that both the temperature and maintenance of the facilities are up to snuff. Hot, moist environments foster the growth of bacteria and fungus. Rooms should be cleaned and disinfected at least once daily; whirlpools should be filtered and brominated regularly.

4. Wear flip-flops and sit on a towel in the sauna and steam room.
Beware of cuts on your body that might make you especially vulnerable to bacteria. 

5. Do not use these facilities on a hot day.