Sickle Cell in Hot Weather: Heat, Dehydration and Staying Safe
Cold gets most of the attention, but hot weather can be just as hard with sickle cell disease. US guidance lists extreme heat, as well as extreme cold and sudden changes in temperature, among the common triggers for a crisis (NHLBI). Most of the risk comes from what heat does to you, mainly dehydration and pushing too hard, so most of the protection is about fluids, pacing and keeping your temperature steady.
Why can heat trigger a sickle cell crisis?
When it's hot, you sweat to cool down and lose fluid faster than usual. If you don't replace it, your blood becomes more concentrated, which makes it easier for red blood cells to sickle and block small blood vessels. Dehydration is one of the triggers the NHS names most clearly (NHS). Heat also makes exercise more demanding, and overexertion is a trigger in its own right.
There's an extra catch with sickle cell disease. Many people's kidneys are less able to concentrate urine, so they lose more water than usual even before the heat adds to it. That's one reason people with sickle cell are often told to be more deliberate about drinking than their friends.
How much should I drink when it's hot?
More than usual, and before you feel thirsty. There's no single number that suits everyone, so agree a daily target with your haematology team, then add to it on hot days, during exercise and when you're unwell. Practical habits help:
- Carry a refillable water bottle everywhere and refill it whenever you can.
- Drink steadily through the day rather than lots at once.
- Check your urine. Pale yellow usually means you're drinking enough; dark yellow is a sign to drink more (NHS).
- Eat water-rich foods like watermelon, oranges, cucumber and soups.
- Keep alcohol off hot days. The NHS advises people with sickle cell disease not to drink alcohol, and it also dehydrates you (NHS).
- If you're sweating a lot for a long time, ask your team whether you need oral rehydration salts as well as water.
Our guide to sickle cell water intake goes into more detail.
How can I stay cool safely?
- Plan around the hottest part of the day, usually late morning to mid-afternoon. Do errands and exercise early or later in the evening.
- Find shade and keep rooms cool with curtains closed during the day and windows open when it's cooler outside.
- Wear loose, light-coloured clothing and a hat.
- Cool down gently. A fan, a cool (not cold) shower or a damp cloth is better than plunging into very cold water or sitting in front of freezing air conditioning straight after being outside. Sudden temperature changes are a trigger too.
- Pace yourself. Take breaks, sit down in the shade and stop if you feel dizzy, sick or unusually tired.
Is a warm climate easier or harder?
It can be both. Many people find steady warmth easier than cold, damp winters. But hot climates bring constant fluid loss, and travel to tropical countries can add infections such as malaria, which can be serious for people with sickle cell disease. If you're travelling somewhere hot, read flying and travelling with sickle cell and speak to your team or a travel clinic well before you go (NHS).
Signs of heat trouble to watch for
Early signs of dehydration include thirst, a dry mouth, dark urine, headache and feeling tired or dizzy (NHS). Heat exhaustion can add heavy sweating, cramps and feeling sick. Move somewhere cool, drink and rest, and follow your crisis plan if pain starts.
- you have severe pain with breathing difficulties, or you're being sick and can't keep fluids down
- you have sickle cell disease and a high temperature
- someone is confused, very drowsy or collapses in the heat
(NHS)
Frequently asked questions
This guide is general information, not medical advice. Always follow the plan agreed with your own care team. Read our medical disclaimer.
Related guides
Why water intake matters with sickle cell disease, what public health guidance says, signs of dehydration, and how to build a realistic daily habit.
Yes, cold and sudden temperature changes can trigger a sickle cell crisis. Why it happens, why to use heat instead of ice packs, and a winter checklist.
What a healthy sickle cell diet looks like, the nutrients that matter, which foods and drinks to limit, folic acid and iron, and a simple sample meal plan.