The body aches and pains after fever are caused by the accumulation of lactic acid in the muscles. Due to the stimulation of the nervous system by viruses and bacteria, pyrogens can cause an increase in the production of inflammatory factors in the body, and the nutrient metabolism of cells in the muscles is blocked to some extent, and the cells do not receive sufficient oxygen supply. The pyrogen acts on the thermoregulatory center and causes motor nerve impulses, causing skeletal muscle spasms throughout the body, while the body temperature rises and the body’s metabolism increases, causing the accumulation of lactic acid in the muscles, resulting in symptoms such as muscle aches and pains. When this symptom occurs, you can take antipyretic and analgesic drugs to relieve this muscle pain, such as ibuprofen, acetaminophen, etc., and also need to take sufficient rest and avoid strenuous activities.