Why does heat make you tired?

3rd June 2019


Have you ever noticed that in hot weather, you regularly feel tired or sluggish? You’re not alone. Heat has been proved to have physical effects on the body that make us feel drained, but the good news is that, once you know the causes, you can do something about it.

Reasons heat makes you feel tired

Body cooling

Your body is always working to regulate your temperature so, in hot weather, it’ll be making adjustments to keep you cool. Even if you’re lying still on the beach, your body is hard at work managing your heart rate and blood flow, as well as sweating to cool your skin. No wonder it gets tired!

Calorie deficiency

All this extra work the body does to regulate temperature burns calories, which means your energy levels will drop quicker than usual and leave you feeling lethargic.


Tiredness is a key symptom of dehydration, and in hot weather we’re more likely to get dehydrated due to the extra work our bodies are doing. As we’re generally used to the amount of fluid we need, it’s common to forget to increase your intake in hot weather.

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Sun exposure

While sunlight is generally associated with waking up, not dozing off, the sun can make you feel tired. Prolonged exposure to the sun can cause further damage to your body. When you get sunburn your body pushes fluid to the affected areas, meaning there’s less to serve the rest of your body. This inhibits your ability to cool down via sweating.

The extreme heat caused by sunburn also makes it harder for the body to gauge its overall temperature, making it more difficult to regulate effectively.

In extreme cases, where you spend a lot of time outside or overexert yourself in the heat, you may even get heat exhaustion or sunstroke. In this instance, you will experience sleepiness along with dizziness, extreme sweating, nausea and a noticeable change in pulse, and should consult a medical professional as soon as possible.

Mind tricks

Sometimes, your feeling of tiredness in the heat could just be your brain playing tricks. For example, we tend to associate warmth with being cosy and comfortable; sensations we usually feel when we’re settling into bed. So when you’re warm, your brain may make the link to bedtime and start to prepare for sleep.

Moving from outdoors to indoors can have a similar effect in summer weather. The contrast between bright sunlight and dimmer indoor lighting could make your brain think it’s dark, triggering the release of sleep hormones.

Lack of sleep

Sometimes, the easiest answer to why we feel sleepy in the heat is simply that we aren’t getting enough rest. In hot weather, our bedrooms tend to get stuffy and we often throw off our thick duvets.

This combination of uncomfortable heat and change in sleeping conditions are likely to leave us tossing and turning all night.

How to avoid it

Drink water

In hot weather we often forget to drink more until we feel thirsty, but the best approach is to drink consistently throughout the day before we start to feel the impact.

Keep a water bottle with you to remind you to drink, and foods with high water content, like fruit and vegetables, will also help to keep you hydrated.

Remember that alcohol is a diuretic that will actually dehydrate you faster than not drinking any liquid at all. If you’re drinking alcoholic drinks in hot weather, remember to balance it out with plenty of water.

Eat salty foods

When you’re sweating more, you lose salt as well as fluids. Snacking on salty foods like crisps or nuts will help to keep your salt levels up. The bonus effect is that the salt will make you thirsty, reminding you to drink your water!

Eat regularly

If your body is burning through calories to regulate your temperature, it’s important to replace them. Many people find their appetites dip in hot weather, but it’s important to keep eating regularly. If you feel like you’re not eating as much at mealtimes, try to supplement this with additional snacks throughout the day or focus on energy-rich foods.

If you can combine this with the above pointers about eating salty and high water content foods, then all the better!

Avoid the sun

Staying in the shade as much as possible will help to reduce the exhausting effects of hot weather. Avoiding direct sunlight will also reduce the risk of sunburn, heat exhaustion and sunstroke.

If you know you’re going to be exposed to the sun, protect your head with a hat and cover up with long, breathable clothes. Bear in mind the areas that are most susceptible to burning, like your shoulders, chest and scalp.

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Slow and steady

Your body is already working harder to regulate your temperature in hot weather, and physical activity only makes this worse. Try to avoid any extreme physical activity in the heat, and take regular breaks to rehydrate and allow your body time to cool down. The heat will naturally make you feel tired, so listen to your body and stop when you need to.

Change your bedding

If you’re struggling to sleep at night in the heat, the first thing you can do is make changes to your bedding. Buy a thinner duvet for summer, or you could even just use an empty duvet cover or thin sheet if your room is particularly stuffy.

Keep your room as cool as possible by opening windows or investing in a fan or air conditioning unit. Closing your curtains during the day to keep the sun out can also prevent your room from getting too hot.

If you regularly find yourself getting too hot at night, consider changing your mattress. Innerspring mattresses are generally best at keeping you cool as they have less foam to absorb heat and maintain good airflow through the springs.

There are a variety of reasons why we often feel tired in the heat, but by managing our body temperature and staying out of the sun as much as possible, we can offset some of the more dramatic effects.