Hot and bothered: how heat makes MS symptoms worse

Around three quarters of people with MS find that their symptoms get worse when they are hot. This could be anytime or anywhere. It's usually noticed during exercise, in busy or heated rooms or when it's hot outside. But why is this, and what can you do to beat the heat?

Any symptoms can flare up in high temperatures, but these are the most commonly affected:

• fatigue
• blurred vision
• poor balance
• trouble with concentration or memory

The effect is temporary and your symptoms should calm down once you are cool again.

There are several possible reasons. 

MS damages some of your nerves. When you get hot, the messages that travel along the damaged nerves may slow down. This can cause your symptoms to worsen. 

For some people, MS damages the brain area that controls temperature regulation in the body. This means that their bodies do not flush or sweat in response to the heat. Flushing or sweating are responses that help to cool you down, so your body temperature rises.

Having an infection can cause your body temperature to rise. You may feel unwell or feverish, but in some cases you might not even realise. Either way, your MS symptoms can flare up and you may feel like you are having a relapse. As you recover from the infection, your body will cool and your MS symptoms will subside.

In the days before MRI scans, lumbar punctures and evoked potentials, the test for MS was immersing someone in a bath of warm water. Doctors would watch to see if the patient's neurological symptoms appeared or got worse. 

This test hasn’t been used for a long time but it's worth remembering if you find that your symptoms get worse when you have a hot bath or shower. If so, it’s best to begin with a tepid shower and then increase the temperature gradually.

If you are heat sensitive, there are a range of things you can do.

• In hot weather, you might go out earlier or later in the day when it’s cooler or keep to the shady side of the street. Avoid sitting in the sunshine for too long or take a broad brimmed hat or sunshade.
• Think about turning down the central heating. This might be popular with the bill payer too! Some people think that it’s a good idea to keep warm if you are unwell. You might like to explain that the opposite is true with MS.
• If you get too hot during exercise or everyday activity, you could opt to go out at the coolest time of day. Research shows precooling yourself can give you more stamina for exertion. This could mean having cold drinks, sucking ice cubes, or taking a cold shower..
• If you are sitting still, you could organise a fan or an air conditioner to provide cooler air.
• Cooling garments are available including neckties and pillows.

Read Ask the expert: heat sensitivity, where we collected more tips for dealing with heat intolerance from people with MS.

• Ask the expert: heat sensitivity. We asked people with MS for their top tips for managing MS in the heat.
• Temperature sensitivity
• Chilled out: cold sensitivity and MS For some people with MS, low temperatures are worse than the heat. 
• What's causing my symptoms?  This tool can help you understand the underlying causes for the MS symptoms you have.
• Top tips for a stress-free summer holiday. Dealing with the heat is just one potential issue for people with MS in summer.
• Uhthoff's phenomenon This is the formal name for heat sensitivity in MS.