Can you get sick?
The good news is that many of these microbes naturally live on the skin and enjoy a peaceful relationship with their hosts—also known as you and me. But in high concentrations, some can cause infection, Tetro says.
The most common troublemaker is Staphylococcus aureus, which can lead to staph infections on the skin. One contagious type of staph infection called impetigo causes red sores and blisters that can ooze and crust.
Other lovely-sounding organisms such as Pseudomonas putida and Acinetobacter baumannii can cause respiratory infections and a more serious skin infection called cellulitis.
Staph infections are typically not serious, unless it is a Methicillin-resistant Staphylococcus aureus infection, known as MRSA. MRSA is resistant to many antibiotics typically used to treat staph infections, and it can be potentially life-threatening if it spreads to the bones, heart or bloodstream, according to the Mayo Clinic.
Other lovely-sounding organisms such as Pseudomonas putida and Acinetobacter baumannii can cause respiratory infections and a more serious skin infection called cellulitis, but these germs usually only affect people with suppressed immune systems, Tetro says.
Ladies, don't hang out in your sweaty shorts after a run.
In addition to being more susceptible to body acne and painful skin chafing, women are more prone to vaginal infections if they stay in their damp gear too long, says Dr. Petra M. Casey, an obstetrician and gynecologist at Mayo Clinic in Rochester, Minn.—and an avid runner.
"Sweaty clothing against the skin may promote overgrowth of certain bacteria or yeast," she says. That can cause bacterial vaginosis, an infection with gray-green vaginal discharge and a fishy odor. Sweaty shorts can also lead to a yeast infection, which causes itching, burning, irritation and white discharge.
Both are easily treated with an antibiotic or antifungal medication, but women should see their doctor for a proper diagnosis if they have these symptoms.
"To help prevent vaginal infections, shower and change into dry, clean clothing as soon as possible after a workout," Casey says—and use an antibacterial or anti-acne shower gel in your acne-prone areas.