When a body is infected with a virus, the immune system works to fight the infection. This fight could lead to muscle inflammation and weakness — called myositis — or joint and muscle pain — called myalgia. Pain manifested in the joints is also commonly associated with a fever, known as arthralgia. Other potential symptoms include fever, muscle aches, and fatigue. Different from COVID-19, a cold does not cause shortness of breath, body aches, chills, or loss of appetite, and it usually doesn’t cause fever. Unlike a virus, a seasonal allergy is caused when the immune system responds to a harmless non-human substance.

The pain, redness, swelling, and heat that result from inflammation are the body’s defense mechanisms to fight off infectious agents like bacteria and repair tissue damage. Whether from a cold, the flu, or COVID-19, acute inflammation is less obvious but similar in process. Older adults are at risk for hypothermia, where the body’s internal temperature falls too low. Even prolonged exposure to mild cold can lead to hypothermia, says Dr. Salamon. Symptoms to be aware of include stiffness in the neck, arms, and legs, and it’s advised to call 911 if these occur.

Less air pressure surrounding the body can allow muscles, tendons, and other tissues around joints to expand, possibly leading to joint pain. On cold, damp days, behaviors that can worsen joint pain or stiffness, such as prolonged sitting, may be more common. Genital herpes infection begins with redness and tingling, followed by small painful bumps that progress to fluid-filled blisters. These then burst to form shallow ulcers, eventually crusting over, with healing over a couple of weeks. Fever, body aches, and fatigue can also accompany an initial genital herpes infection.

Intermittent fasting may produce side effects like headaches, lethargy, crankiness, and constipation. To decrease these effects, switching from alternate-day fasting to periodic fasting or a time-restricted eating plan is suggested. Cold weather, while hard on health, can have benefits by killing off disease-mongering organisms.

In the context of muscle and joint pain during flu, the key points from NewsCOVID-19 and Harvard Health emphasize the role of the immune response and inflammation. As per Harvard Health, cold weather can exacerbate these symptoms, while Harvard Health discusses the symptoms of genital herpes. Furthermore, Harvard Health informs about intermittent fasting side effects, which can also include muscle aches.