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Hot and bothered: how heat makes MS symptoms worse

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man asleep on bed

Around three quarters of people with MS find that their symptoms get worse when they are hot. This might be when the summer weather arrives, during exercise, when the central heating is too high or if you are in public spaces which can be overheated.

It is common to experience increased fatigue, blurred vision, poor balance or more trouble with concentration or memory but any symptoms can flare up. The effect is temporary and symptoms should calm down once you are cool again.

Colds, flu and other infections

Many infections cause the body’s temperature to rise. You may realise that you have a fever or you could just feel unwell. Either way, MS symptoms can flare up and you may even feel like you are having a relapse. However, as you recover from the infection, the symptoms will subside.

The hot bath test

Amazingly, in the days before MRI scans, lumbar punctures and evoked potentials, the test for MS was immersing someone in a bath of warm water to see if their neurological symptoms appeared or got worse. This test hasn’t been used for a long time but it can be 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 decrease the temperature gradually.

What causes heat sensitivity?

There are several possible reasons. In many people with MS, getting hot slows down the messages passing along nerves which have already been damaged by MS and this gives rise to increased symptoms. In some cases, there is a lesion in a part of the brain that controls temperature regulation in the body. Other people might have a lesion in a brain area that should respond to increased temperature, for example, by initiating sweating or sending more blood to the skin so you cool down again. In both cases, the poor response means that body temperature rises.

Keeping your cool

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. You could avoid sitting in the sunshine for too long, wear layers of clothes that you can peel off, take a broad brimmed hat or a sunshade.
  • If the family likes to have the central heating up high, you might negotiate turning it down and encourage them to wear an extra layer. This might be popular with the bill payer too. Some people think that, if you aren’t well, it’s a good idea to keep warm. 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. You can precool yourself by having cold drinks, sucking ice cubes, taking a cold shower or spraying yourself with cool water.
  • 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. 

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