You wake up with a headache and a scratchy throat — telltale signs of an oncoming cold. Normally you hit the gym every morning, but if you’re getting sick, will hefting weights or sweating on the treadmill hurt you?

In some cases, exercising while sick can be perfectly fine. In others, it can be a not-so-smart move. Next time you’re under the weather and not sure if you should push through your CrossFit session or limit your activity to spooning chicken soup into your mouth, keep these guidelines in mind.

Go ahead and sweat if…

  • Your symptoms are above the neck. “If you have a minor cold or respiratory illness, you should be fine,” says family physician (and passionate weight lifter) Spencer Nadolsky, DO, of Olney, Maryland. Symptoms such as a runny or stuffy nose, minor sore throat and sneezing shouldn’t prevent you from lacing up your sneakers or rolling out your yoga mat. In fact, activity may even help to open nasal passages and relieve congestion, according to the Mayo Clinic. Sweating won’t rid your body of toxins, however. That’s a myth.
  • You don’t have a fever. When the thermometer's in the red, stay in bed.
  • You’re truly up for it. “Let your body be your guide,” advises Nadolsky. “If you don’t feel too lousy to exercise, go ahead and follow your regular routine. Or, dial it back a bit — instead of a long run, go for a short walk. Take a Pilates class instead of doing Zumba.”

Related: 5 Fast Ways to Unclog a Stuffy Nose

Play exercise hooky if…

  • You’re sick from the neck down. Give yourself a break if you have chest congestion, a hacking cough, gastrointestinal symptoms like nausea, vomiting or diarrhea, body-wide fatigue or achiness, swollen lymph glands. says Nadolsky.
  • You have a fever. Use the excuse to rest up.
  • You may be contagious. If you think there’s any chance you could pass your illness along to other folks, the National Institute for Fitness and Sport (NIFS) recommends you stay home. Germs love to hang out on gym equipment. Keep in mind that different illnesses are contagious for varying amounts of time. According the NIFS, a stomach virus can be contagious for up to two weeks after recovery.
  • You have a condition or symptoms that could get worse if you exercise. These include respiratory infections, which can be aggravated with intense cardio activity, migraine and serious headaches and severe body aches, according to NIFS.
  • You’re taking cold medicine that makes you drowsy. Many over-the-counter cold, cough and flu remedies containing ingredients that can leave you feeling foggy, such as pseudoephedrine. If you aren’t able to pay full attention to what you’re doing you could injure yourself with a piece of equipment or have trouble maintaining safe form while you exercise.

Related: Checking Kids For Fevers: Which Kind of Thermometer is Best?

Get back to working out...

  • Once you’re feeling better and, if you had a high temperature, you’re fever-free. Don't go to the gym or take classes unless you're no longer contagious.
  • But start slow. Dial back the intensity and length of your regular routine a bit at first. But do get back to your workouts. Studies show regular activity boosts immunity, so while an apple a day won't hurt, exercise is the best way to keep the doctor away.

Related: Can't Get Into the Exercise Habit? Try this Trick

Denise Foley is a veteran health writer and a former contributing executive editor at Prevention magazine.