Heat intolerance: What are the symptoms, causes and treatment?

Does heat affect you more than most? Here’s everything you need to know about heat intolerance

Heat intolerance is a condition where the body can’t regulate its internal temperature properly. This can lead to a higher risk of developing heat stroke, which can be life threatening. Some conditions are known to lower your tolerance to heat and make you more susceptible to overheating, so people with these need to be extra cautious in summer or in hot environments.

We’ve spoken to medical experts about heat intolerance to get their views on the causes, symptoms and possible treatments, as well as their best advice for those with underlying conditions that might put them at higher risk. If you’re worried about getting hot and bothered, we’ve also put together a list of ways to stay cool in the heat and how to stay hydrated.

WHAT IS HEAT INTOLERANCE?

“Heat intolerance (HI) is a disorder of thermoregulation,” explains Dr Deborah Lee, MD, from Dr Fox Online Pharmacy(opens in new tab). It’s a serious condition, which increases the risk of heat stroke. The body cannot function when it gets too hot. Being overheated causes cells to die, blood becomes hypercoagulable and more likely to clot, and the gut starts to leak toxins into the bloodstream. Organs start to fail, and irreversible brain damage can occur.”

A review in Pediatrics in Review(opens in new tab) warns that there is a difference between fever and heat stroke, as the body is still in control of thermoregulation even when feverish, but with heat stroke it loses that control. The review also states that if a child’s core temperature rises above 105.8F (41C) for more than a short time, they are at risk of thermal injury.

Dr Tariq Mahmood, MD, medical director of Concepto Diagnostics(opens in new tab), explains more: “People with heat intolerance experience an unusual level of sensitivity to heat. It isn’t a disease in itself, but there are a number of conditions that can cause someone to suffer from it and it can also be a symptom of an underlying medical condition.

“A person with heat intolerance can experience physical symptoms such as increased sweating, or psychological symptoms like feelings of anxiety. It’s important to listen to your body when in direct heat, as heat-related illnesses are prominent during the summer and can be fatal in acute cases.”

Dehydration is another risk when someone is too hot, according to Johns Hopkins Medicine(opens in new tab). If you are on diuretic medication you should be careful to avoid dehydration, as this can cause more frequent urination, ridding your body of salt and water. Extreme dehydration may need to be treated with intravenous (IV) fluids, so it’s important to seek medical help if you think you may be severely dehydrated.

WHAT CAUSES HEAT INTOLERANCE?

Lee says that a few conditions can cause heat intolerance. “In some individuals, HI may be due to genetic alterations meaning the person has a lower exercise tolerance in moderate heat,” she says. “Other cases of HI may be linked to dysautonomia, which occurs in association with a range of diseases that affect the nervous system. These include:

Alcoholism

Autoimmune diseases

Diabetes

Ehlers Danlos Syndrome

Guillain Barré Syndrome

HIV

Long Covid

Multiple sclerosis

Spinal cord injuries and traumatic brain injuries

Dementia

Parkinson’s disease

Lee says that heat intolerance is also more common in those with sympathetic nervous system dysfunction. Conditions include:

Chronic fatigue syndrome/ME

Fibromyalgia

Irritable bowel syndrome

Mahmood says that diabetes in particular can lead to dangerous levels of heat intolerance. “People with diabetes are at a higher risk of suffering from heat exhaustion and can also be more prone to heat intolerance,” he says. “Diabetes complications can include damage to blood vessels and nerves, subsequently affecting sweat glands, making the body unable to cool as effectively as it usually would.

“Unfortunately, in instances like these, heat intolerance isn’t treatable or preventable, but people are able to protect themselves and take proactive steps to avoid finding themselves in particularly warm situations.”

WHAT ARE THE SYMPTOMS OF HEAT INTOLERANCE?

Mahmood says that individual experience of heat intolerance can vary, but some symptoms are more common than others. “Heat intolerance symptoms vary on a person-by-person basis, but can include feeling uncomfortably warm when in moderate temperatures, fatigue, exhaustion, nausea, vomiting, mood swings or even not sweating enough in the heat,” he says. “People with chronic illnesses like multiple sclerosis can experience worsened symptoms when in high temperatures and people with endocrine system problems, such as a thyroid condition, can struggle in heat as the body isn’t able to regulate itself.”

According to Lee, the most common symptoms of heat intolerance include:

Feeling hot and uncomfortable when the temperature is only slightly raised

Feeling light-headed or dizzy

Headaches

Feeling weak and tired

Muscle cramps

Nausea and sometimes vomiting

Rapid heartbeat

Excessive sweating

Inability to sweat

CAN YOU TREAT HEAT INTOLERANCE?

Heat intolerance is not something that can be treated with medication, but there are measures you can take to reduce the risk of overheating:

Take a cold shower or bath

Use cold washrags or ice packs on your neck and wrists

Run a fan or air conditioning when you sleep

Close your curtains or blinds to create a shade

Don’t go out in the sun for long periods of time

Drink plenty of water, iced water will keep you cool as well as hydrated

Sleep in breathable linens

“The first step in treating HI is to recognise you are at risk,” adds Lee. “If you have any of the above underlying conditions, HI may well be a problem for you, so you need to be aware. You need to plan ahead to adopt measures to prevent yourself from overheating. It’s also imperative that any underlying medical conditions are treated.”