Handling the heat - latest research

What is heat sensitivity?

Many people with MS find that their symptoms get worse in the heat. This can be triggered by hot baths, the sun, or exercise.

The effects of heat are temporary, but heat sensitivity can be extremely unpleasant. It can have a massive impact on day-to-day activities like working, exercising, or even taking a walk on a warm sunny day.

Why does it happen?

Changes in temperature can affect the way our nerves function and make it more difficult for them to send messages.

This is even more true when the myelin coating around nerves is damaged, as it can be in MS. That’s because as well protecting nerves from damage, myelin also shields nerves from changes in temperature.

We still don’t fully understand why nerves without myelin are less able to cope with increases in temperature. But researchers have found that raising body temperature by as little half a degree Celsius can aggravate MS symptoms.

What‘s the latest in heat sensitivity research?

Researchers in the US are investigating how our bodies regulate temperature and if this can affect heat sensitivity in MS.

There’s some evidence to suggest that people with MS can’t regulate body temperature as well as those who don’t have MS. This may mean their core body temperature increases more quickly, triggering heat sensitivity.

A team in Australia is also developing new ways to keep cool during exercise. This would help prevent people with MS getting heat-related fatigue.

I’ve been really lucky to work with both of these groups. Together we’re aiming to understand more about the biology of heat sensitivity. We’ll then use this knowledge to develop more effective solutions for it.

What are you working on?

I’m particularly interested in how heat sensitivity is triggered in MS.

We typically find that a high internal (core) body temperature can affect the way nerves work. But a lot of people with MS find that just being in the sun can worsen symptoms like fatigue.

This could mean that an increase in skin temperature is enough to trigger symptoms. My team is working to understand how changes in skin and core body temperature can affect MS symptoms like altered sensations and problems with memory, thinking and movement.

We also want to understand why exposure to cold can worsen MS symptoms.

Do you have any tips for dealing with heat sensitivity?

Research has highlighted the benefits of ‘pre-cooling’, which basically means cooling down before exercise to help combat temperature rises. This could mean having a cool bath or a cold drink before exercising or going out when it’s hot.

There are also cooling vests that you can wear during exercise or in the summer. Some people find them uncomfortable, but they might be worth a try if you’re particularly sensitive to heat.

Research update

Davide's continued researching heat sensitivity since writing this blog. In 2020, Davide and a team of researchers looked at core temperature and differences in heat regulation between people with MS and people without.

They asked a small group of people with MS to cycle at 35 degrees celsius. The team measured the participants’ ability to sweat as a way of looking at how well they can cool down.

They compared this to a small group of people without MS. People with MS started sweating later than people without when exercising in the heat. But their core temperatures still changed at the same rate. So the difference in sweating is not the reason for heat sensitivity. 

In 2023 Davide and his team published the results of a study that compared how people with and without MS experience different temperatures. They heated up the room temperature to 39 degrees celsius or cooled it down to 12 degrees celsius. At the same time they recorded the participants’ physical responses, for example body temperature, heart rate and blood pressure. They also recorded if the participants felt any mental and physical discomfort. And they used a cognitive test to see how well the participants were able to process information.

They found the physical responses did not differ between people with and without MS. And they found that the information processing was not affected by the cold or heat. But they found more people with MS than people without MS felt uncomfortable at the end of the heat period. And people with MS reported feeling more mentally and physically fatigued during the heat and the cold period.

Davide and his team think discomfort and fatigue experienced by people with MS could be one of the reasons for MS heat and cold intolerance.