Why Do You Experience Muscle Pain When You're Sick?

Muscle aches are a common flu symptom—but why do they happen when you're under the weather?

When illness strikes, your immune system activates. White blood cells release interleukins, signaling molecules that rally other immune cells body-wide. These can accumulate in muscles, triggering pain. It's akin to exercise-induced soreness from lactic acid buildup, but here it's immune signals at work.

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