Medically reviewed by Joseph V. Campellone, M.D.
Written by Emily Brown
If you’re sensitive to temperatures — especially heat — and your multiple sclerosis (MS) symptoms feel worse when you have a fever, you’re not alone. MS causes damage (called demyelination) to the myelin sheaths of nerve cells in the central nervous system. A higher body temperature makes it harder for axons of demyelinated nerves to send electrical signals. Even small increases in core body temperature can cause MS symptoms to get worse.
People experiencing inflammation related to MS tend to have warmer body temperatures than those without MS. Certain medications for MS may also cause infections (which may result in fevers) as a possible side effect. The definition of a fever is an internal body temperature at or above 100.4 degrees Fahrenheit (38 degrees Celsius). Because fever can make MS symptoms feel worse, it’s helpful to understand the underlying causes of fever, how to manage fever, and when to seek medical attention.
Can Fevers Make MS Symptoms Worse?
Heat sensitivity or fever can make old MS symptoms pop back up or existing symptoms feel worse.
Some symptoms that may worsen include balance issues, fatigue, vision impairment, and cognitive problems. About 60 percent to 80 percent of people with MS experience worsening neurologic symptoms and clinical signs (changes in the normal healthy state) with exposure to heat. Some MyMSTeam members also describe worsening muscle aches and pain, muscle weakness, and movement problems with heat sensitivity:
- “I had a very high temperature a year ago. I couldn’t move my left leg, and my left hand was really clumsy.”
- “I had two bladder infections where I ran a temp. Both times, the fever affected my MS. I couldn’t stand, kept collapsing.”
- “Having a fever causes me to be numb.”
- “Got a sinus infection and fever. My MS is OK, but when I get a fever, I can’t move so well.”
- “I’m confused whether my myalgia is due to the fever, or if the fever has worsened my usual MS symptoms.”
The worsening of MS symptoms with fever is usually temporary. Once the body cools and gets back to a normal temperature, symptoms should reduce to the level that’s normal for you.