If you’re like most guys with a home gym, your equipment is tucked into some unused corner of your basement or garage. That’s a problem, because when you work out in those spaces you’re exposing yourself to dangerous pests, pollutants, and other hazards that can threaten your health–or even your life, explains Janice Nolen, an air-quality expert with the National Lung Association.

Here, Nolen lays out the most common threats you’ll likely encounter while working out at home–and what you can do about them.

Radon

The threat: This invisible, radioactive gas occurs naturally in the ground when uranium breaks down–a process that takes millennia, Nolen says. It’s also the number one cause of lung cancer among non-smokers.

Radon is everywhere. But the real danger exists when large concentrations of the gas build up in poorly ventilated spaces at or below ground level–like in your basement, Nolen says. Add to that the fact that your breathing rate triples or quadruples when you exercise (meaning you’re sucking a lot more air into your system), and the danger is compounded, Nolen says.

The fix: The only way to know if you’re at risk is to have your place tested.

“You may have heard that your neighborhood is at low-risk for radon. But even if your next-door neighbor tested negative, that does not mean your home is safe,” Nolen stresses.

You can have a radon inspector check out your home, or you can pick up a mail-in kit from your local hardware store. If your test turns up dangerous levels, you’ll have to pay to have a system installed to remove the gas from your air, Nolen says.

Protect your bacon with these 8 Small Measures that Can Save Your Life.

Fossil fuel fumes

The threat: You probably keep a lot of chemicals in your garage–including gas for your lawnmower or oil for your car. And if you can smell any of those substances, those fumes could cause serious health issues, Nolen says.

In the short term, you may feel light-headed or dizzy, or have an irritation in your nose, throat, or eyes. In the long run, exposure to some of these chemicals–like benzene or 1,3-butadiene–can cause bone marrow and blood disorders, as well as cancer, according to the Centers for Disease Control and Prevention (CDC).

The fix: Apart from keeping an airtight lid or cap on your chemical containers, opening windows and doors to let the fumes disperse can help, Nolen says. But if you keep a car alongside your workout equipment–or if you smell anything gassy in the air–that’s not a safe area to be working out.

Pests

The threat: Garages and basements tend to be warm and humid–especially in summer–which creates ideal breeding conditions for pests and germs, Nolen says. Cockroaches spread illness-causing bacteria like salmonella, and also carry antigens that trigger asthma attacks. Dust mites are also common in humid spaces, Nolen says. Like roaches, they can cause respiratory problems. (They also infest your eyelashes.)

The fix: Apart from improving ventilation in your space with exhaust systems or window ventilation fans, a dehumidifier can help suck the moisture out of the air, making the space less hospitable to critters, Nolen says.

“Your target is to lower the humidity below 50 percent.”

Mold and fungus

The threat: Like pests, molds and fungi love moisture-rich environments. They also cause breathing problems, headaches, stuffiness, and infections, Nolen says.

How do you know if mold is present? Trust your nose. If your basement smells generally funky–and especially if it has a distinctly dank odor that you don’t notice anywhere else in the house–mold is probably present, Nolen says. You also may be able to spot it in corners, on pipes, or under carpeting. (Look for furry splotches.)

The fix: If you’re pretty sure the mold is only in one spot, you can clean it up yourself with soap and water–no bleach necessary, Nolen says. Just be warned: Disturbing the mold can release spores into the air, which could trigger all the health issues listed above. If you’re not sure how much mold is present, you’ll need to call in an expert to check and help you remove it. Once the problem’s resolved, keeping your basement ventilated and the humidity low will help stop mold from reappearing, Nolen adds.

Use these smart antimicrobial strategies to Eliminate Germs in Your House.

Volatile organic compounds (VOCs)

The threat: Paints, lacquers, cleaning supplies, and other types of home-improvement products contain these compounds, which escape in the form of gas. And, if you’re like most people, you probably keep these materials stacked in one area of your basement or garage, which concentrates their emissions, Nolen says.

Along with eye, nose, throat, and lung irritation, VOC gases can cause long-term damage to your kidneys, liver, and central nervous system, according to the Environmental Protection Agency.

The fix: Move them into well-ventilated areas away from places where you’ll be hanging out, and make sure they’re tightly capped or sealed to prevent exposure, Nolen advises.