As if chills, a fever, and a faucet of a nose weren’t enough, the flu brings along yet another common (and very uncomfortable) side effect: body aches. In fact, these aches are one of the telltale signs that you’re about to be OOO the next day.

But what’s going on inside your body to cause this muscle soreness when you’re super sick? It’s not only the work of that nasty virus, interestingly enough.

“Your body aches when you have the flu because your immune system is revving up to fight infection,” said Dr. Tania Elliott, MD FAAAAI, FACAAI, associate attending at NYU Langone Health in New York City, and national spokesperson for the American College of Allergy, Asthma, and Immunology

“When this happens, it releases chemicals called inflammatory cytokines that have virus- and bacteria-killing properties. With this, though, comes inflammation in your muscles and rest of your body. They also cause your core body temperature to rise, resulting in fevers.”

So that dull, seemingly endless ache is actually the side effect of the cytokines (released by white blood cells) fighting off germs.

Many cytokines are released during your immune system’s response to a virus, but according to Dr. William W. Li, M.D., author of Eat to Beat Disease: The New Science of How Your Body Can Heal Itself, one important player in the ache-causing inflammation is interleukin-6.

“Your achy muscles force you to slow down so your body can focus on recovering,” Dr. Li explained. “Fortunately, this usually lasts only about a week in most cases, and then the immune attack is turned off, levels of cytokines like interleukin-6 go down, and the muscle aches stop, you feel better, and can go on with your ordinary activities.”

If you do feel body aches coming on, it could be more serious than just a little Winter cold.

“The onset of fever and aches warns people that they have the flu, and it is a good idea to see the doctor to get treatment,” said Dr. Elizabeth Landsverk, MD, adjunct clinical professor at Stanford University School of Medicine.

If the flu is treated within the first 48 to 72 hours, Dr. Landsverk said, certain over-the-counter medications may decrease the severity of symptoms, but she also noted it’s better to have had the flu vaccine.

Dr. Li recommends allowing your muscles to relax, staying hydrated, and drinking a relaxing hot beverage, like chamomile tea, to help calm your body. And if the aches get too bad, a nonsteroidal anti-inflammatory medicine may offer some relief.

“Chicken soup has also been researched and was found to contain natural chemicals that temper the effects of inflammation — so Grandma was right. Avoid eating ultraprocessed foods and fatty foods, which can damage your gut bacteria and amplify inflammation in ways you don’t need. Stay away from alcohol, which also amplifies the inflammatory response and will make you feel crappy,” Dr. Li added.

Overall, it’s always a smart idea to call your doctor when you have body aches to ensure you’re getting the best treatment possible.

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