When you're feeling under the weather, you might wonder whether pushing through a workout will help you get better faster or make your illness worse.

Exercise helps build and maintain a healthy immune system, after all. But on the other hand, you've likely also heard that getting plenty of rest is key for recovery.

So which is it when you're sick?

"While physical activity is important for overall health, exercising while sick requires some caution," says Dr. Donald Brown, an internal medicine hospitalist at Houston Methodist. "Always check with your doctor if you're unsure whether it's safe for you to exercise."

That said, there are useful general guidelines anyone can follow. Here's when it's probably OK to exercise, when you should take a break and how to adjust your routine if you do decide to work out.

Should you exercise when sick?

Whether the affliction is a common cold, the flu, COVID-19, an upset stomach, an earache or something else, the first step is to consider your symptoms.

"The general rule of thumb for exercising while sick is that if your symptoms are above the neck, you can likely continue with your routine — but at a lower intensity and shorter timeframe," explains Dr. Brown. "Be sure to listen to your body and be mindful of how you feel."

This means it's probably OK to push through if you're dealing with a:

• Runny or stuffy nose
• Nasal congestion
• Sneezing
• Mild sore throat
• Light headache
• Mild earache

Start with light to moderate physical activity. Options like walking, yoga, or a short, low-impact workout — light swimming, cycling, rowing, jogging, bodyweight movements — can help get your blood flowing without the risk of overworking your body.

"A little exercise might even temporarily improve certain symptoms, like nasal congestion," adds Dr. Brown. "However, if you feel worse after starting, it's best to stop." (Related: How to Get Rid of Congestion)

Can you exercise while taking cold medication?

Even if your symptoms are mild and above the neck, the medications you're taking could be a reason to take a pause.

"Multi-symptom cold medications almost always contain phenylephrine, an oral decongestant that can affect heart rate and blood pressure," says Dr. Brown. "This might make exercise seem more strenuous than usual. The most important caution here is for people with preexisting heart conditions. Always check with your doctor before taking a new over-the-counter medication and heed any warnings."

(Related: That Decongestant In Your Cold & Allergy Medications Likely Doesn't Work)

Other medications, like antihistamines, can cause drowsiness, which could make it harder to stay focused and coordinated during your workout. Always check the side effects of a medication before working out and, when in doubt, choose rest.

Skip your workout if ...

When symptoms are below the neck, Dr. Brown says rest is the best medicine. And know that a few days of skipped workouts shouldn't significantly affect your performance once you're feeling better.

Avoid working out if you have a:

• Fever
• Body aches or chills
• Chest congestion
• Persistent cough
• Nausea
• Vomiting
• Diarrhea

"Exercise can exacerbate chest congestion and gastrointestinal symptoms," explains Dr. Brown. "And if you're experiencing fever, significant fatigue and difficulty breathing, it's best to rest and allow your immune system more time to do its job."

If you feel up for it, you can consider doing some dynamic stretching — active movements that can help keep your body loose without overdoing things. Examples include arm circles, lunges, torso twists and high knees. (Related: The Benefits, Do's & Don'ts of Stretching Correctly)

How to modify your workouts while sick

If your symptoms are mild and above the neck, and you decide to exercise, consider these modifications that can help keep you from overexerting yourself:

• Lower the intensity: Skip any high-intensity workouts. Opt for exercises like walking, light jogging or yoga.
• Reduce the duration: Don't push yourself through a full workout if you're not up for it. Consider reducing the duration of your typical workout, perhaps even by half or more.
• Prioritize active recovery: Remember your body needs rest. If you feel like you're not getting enough out of your modified workout, add recovery exercises like dynamic stretching, deep breathing, foam rolling or tai chai.

"Your goal should be to move in a way that feels good without pushing your body too hard," recommends Dr. Brown. "Pay attention to your energy level and stop if you feel lightheaded or overly fatigued."

Hydration is always important, but even more so when you're sick. Be sure to drink plenty of water before, during and after your workout. While you shouldn't be exercising at an intensity that causes a lot of sweat, sip on a sports drink or electrolyte beverage if needed, especially if you have diarrhea. (Related: How Much Water Should You Drink In a Day?)

As your symptoms start to improve, avoid jumping right back into your usual routine. Ease back into things instead.

"Gradually increase intensity and duration, monitoring how you feel along the way," says Dr. Brown. "If you notice symptoms like excessive fatigue, dizziness or shortness of breath, scale back your efforts." You may also consider adding in an extra rest day between workouts as you recover.