It's no secret that gyms are full of bacteria during cold season — antimicrobial wipes and towels can only do so much to keep equipment clean.

But don't be so quick to skip your workout next time.

Your risk of contracting a cold or flu actually drops a bit if you exercise regularly at moderate intensity, said Dr. Edward Laskowski, the co-director of Mayo Clinic Sports Medicine.

"We don't know exactly why, but exercise promotes good circulation, and when you have improved circulation, you can circulate the immune cells that fight disease and infection more rapidly," Laskowski said. "The risk of a cold or flu can actually, if you're exercising regularly, be less."

The big takeaway? Gyms, like any other confined, traffic-heavy area, tend to collect bacteria. Some of it is benign, and some of it is disease-causing.

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But if you want to be healthy, working out should still be the priority.

"In general, we still are, in the United States and globally, in the middle of an epidemic of obesity and sedentary lifestyles," Laskowski said. "Seventy percent of our country is either overweight or obese … so it's a public health crisis. So we want to get people moving."

There are many ways to exercise in the winter, Laskowski, a specialist in physical medicine and rehabilitation, said — at home, outside (dependent on weather-appropriate clothing), or at the gym.

If you prefer to exercise at the gym, there's nothing wrong with that, Laskowski said — just remember that there could be 50-plus people using a given exercise bike in the space of a day.

"When you're using the equipment, make sure you're cleaning it off before you're using it … remember to do the basics," Laskowski said. "Wash your hands and don't touch your face, because mucus membranes are what can transmit the bacteria."

And stay away from other people who seem sniffly, Laskowski said, especially if they're not covering their mouth and face while sneezing or coughing.

Now let's say you've already got a cold. Can you still work out?

"We have a saying — above the neck vs. below the neck," Laskowski said. "If the symptoms are usually above the neck, and it's a runny nose, stuffy nose, usually it's OK to do some light or moderate exercise. And actually, exercise can kind of help clear your nasal passages out a bit and improve things.

"If it's below the neck, if you have congestion in your chest or lungs, if you feel achy in all your muscles, if you have a fever, that may be a sign of the flu or bronchitis, or another, more significant problem. Those, you want to rest," Laskowski said. "If you exercise with a fever, you're going to be more dehydrated, and your body's already trying to fight the infection — that's why you have a fever. And if you stress it more with exercising, you'll make it worse."

While light exercise can be helpful if your illness is mild, Laskowski said that if symptoms include "a lot of discharge," it's considerate to exercise alone for a while, so others aren't inadvertently exposed to your germs.

There is also a caveat to the wisdom that exercising can reduce your risk of getting sick.

Intense, long-duration exercise like a marathon will actually make you more vulnerable to illness for a short time.

"There's a little period of immunosuppression where the immune response is actually blunted a little bit," Laskowski said. "You've done this super maximal exercise, it really taxes your system. You want to get some recovery time after you do something like that."