A spike in body temperature can turn a typical day with multiple sclerosis (MS) into a challenging ordeal. When you have a fever or changes to your normal body temperature, you may notice that the symptoms of MS can quickly intensify. Understanding what causes fever, ways to manage it, and when to seek medical attention may make it easier to cope with temperature sensitivities.

Does MS Cause Fevers?

For the most part, a fever occurs when the internal body temperature is higher than normal, or roughly above 100.0 to 100.4 degrees Fahrenheit (37.8 to 38.0 degrees Celsius).

MS lesions (damage) can occur in areas of the brain that are responsible for regulating body temperature and the body’s response to changes in temperature. This is why many people with MS experience heat or cold sensitivity, although MS itself doesn’t necessarily cause fevers. Some people with MS may have higher body temperatures more often than others. People experiencing inflammation related to MS tend to have warmer body temperatures than those without MS.

Multiple Sclerosis and Low-Grade Fever

Research has shown that people with relapsing-remitting MS (RRMS) tend to have a higher body temperature, possibly due to inflammation related to RRMS. Although not high enough to be considered fever, elevated body temperature in people with RRMS has been linked to worsening general and physical fatigue, which may make MS symptoms more noticeable.

MyMSTeam members have reported recurring mild fevers. “I seem to get random low-grade fevers that make my MS symptoms worse,” shared one member.

“I also have that issue,” replied another. “I mean really low-grade, like 98.9 degrees Fahrenheit. I can tell because I feel wiped out and my vision is messed up. It’s so frustrating!”

Can Fevers Make MS Symptoms Worse?

Heat sensitivity or fever can make old MS symptoms pop back up or existing symptoms feel worse.

MS causes damage, known as demyelination, to the myelin sheaths (protective nerve coverings) of nerve cells in the central nervous system. A higher body temperature makes it harder for axons (nerve fibers) of demyelinated nerves to send electrical signals. Even small increases in core body temperature can cause a worsening of symptoms.

Approximately 60 percent to 80 percent of people with MS experience temporary worsening of neurological symptoms when they are exposed to heat or when their body temperature rises. This phenomenon, known as Uhthoff’s phenomenon, can affect:

• Balance and coordination
• Fatigue levels
• Vision
• Cognitive function (brain processes like thinking, memory, and attention)
• Muscle strength and control

Some MyMSTeam members also describe worsening myalgia (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.

Do Fevers Worsen MS Disease Activity?

Although fevers can make MS symptoms feel worse, they do not indicate increased disease activity. A temporary worsening of symptoms due to fever is not the same as clinical worsening, which involves new or larger lesions, detectable demyelination, or measurable nerve damage. A symptom flare-up without worsening disease is sometimes called a pseudoexacerbation or Uhthoff’s phenomenon, as defined above. When symptoms do flare, it’s important to check for a fever, because a minor infection could be the culprit. For example, urinary tract infections (UTIs) are a common type of infection known to trigger MS symptom flare-ups.

Does MS Make You More Susceptible to Illness?

Certain disease-modifying therapies (DMTs) for MS affect immune system function, potentially causing side effects like fever or increasing susceptibility to infections that cause fevers.

According to the Multiple Sclerosis Centers for Excellence, some common DMTs that list fever as a common side effect include:

• Alemtuzumab (Lemtrada)
• Interferon beta-1a (sold under brand names including Avonex and Rebif)
• Interferon beta-1b (Betaseron, Extavia)
• Ofatumumab (Kesimpta)
• Peginterferon beta-1a (Plegridy SC)

Because DMTs modify aspects of the immune system to reduce MS attacks, infections are common side effects of many DMTs. An infection may lead to fever as the body tries to fight off the virus or bacteria. Below are DMTs that list infections as a common side effect, including the type of infection they may be associated with:

• Alemtuzumab (Lemtrada) — Herpes viral infection, human papillomavirus (HPV), fungal infection, and tuberculosis
• Cladribine (Mavenclad) — Respiratory infection and herpes infection
• Mitoxantrone (Novantrone) — Upper respiratory tract infection, UTI, and stomatitis
• Natalizumab (Tysabri) — UTI, lower respiratory tract infection
• Ocrelizumab (Ocrevus) — Respiratory tract infection and herpes infection
• Ofatumumab — Upper respiratory tract infection and UTI
• Ozanimod (Zeposia) — Upper respiratory tract infection and UTI
• Ponesimod (Ponvory) — Herpes infection and meningitis

MyMSTeam members have shared their experiences about fever as a side effect of DMTs. One member said, “I started an injected biologic DMT yesterday, and wow, I’m definitely having those flu-like symptoms. Can’t get rid of this fever!” Another shared, “My interferon shots for MS used to cause fevers.”

If you’re experiencing fever and wonder if it’s related to your medications, talk to your healthcare provider or neurologist. They can help you figure out what may be causing fevers and how best to manage them.

Tips for Managing Fevers With MS

Managing fever is important for your body overall and especially for reducing the effect of worsening MS symptoms. The main goal when you have a fever is to keep your core body temperature as close to normal — around 98.6 degrees Fahrenheit (37 degrees Celsius) as possible. Make sure you have a thermometer at home to monitor your temperature.

Depending on the severity of the fever, it can usually be managed at home. Talk to your healthcare provider about over-the-counter medications and other strategies to keep your temperature down when fever strikes.

If you notice fevers as a side effect of your DMT, ask your doctor how to prevent them. One MyMSTeam member wrote, “When I was on an injectable DMT that caused flu-like symptoms, my neurologist told me to take over-the-counter painkillers after the injection to ward off any flu-like symptoms and it worked.”

Be sure to consult your doctor before adding any medications, even those available over the counter, to avoid dangerous drug interactions.

Tips for managing fevers at home include:

• Drink plenty of clear fluids.
• Keep your temperature consistent — Avoid extreme changes in temperature, such as going from an air-conditioned room to hot weather outside.
• Rest as much as you need, especially because elevated body temperature can increase fatigue.
• If you experience multiple sclerosis cold chills with your fever, warm up gradually. Adding too much heat quickly can increase your temperature too much.
• If your temperature spikes, cool down gradually with a cool cloth, a lukewarm shower, or special cooling equipment like a cooling vest.
• To help manage your temperature at night, keep blankets by your bed to add on or peel off as needed.

When Is MS-Related Fever Life-Threatening?

While fever typically causes symptoms to temporarily get worse, you should seek immediate medical attention as soon as possible if you have the following symptoms:

• Fever above 104 degrees Fahrenheit (40 degrees Celsius)
• High fever for more than three days without breaking
• Rash
• Extreme confusion or impairment
• Severe headache
• Neck stiffness
• Difficulty staying awake
• Severe diarrhea
• Sensitivity to light

Fever may also be a sign of other conditions, such as respiratory infections or COVID-19. If you are experiencing fever with other COVID-like symptoms, consider taking an at-home COVID-19 test or scheduling a test at a local testing site or your doctor’s office.

Talk With Others Who Understand

MyMSTeam is the social network for people with MS and their loved ones. On MyMSTeam, more than 218,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS.

Do you experience frequent fevers, or are your MS symptoms worse when you have a fever? Have you found effective ways to manage fevers? Share your experience in the comments below, or start a conversation by posting on your Activities page.