The first properly warm week of the year and suddenly your shoes do not fit the way they did in April. Sandal straps leave marks. Your feet look wider. By the evening there is a clear ridge where your sock sat, and you have not done anything differently.
This is common enough to have a name. Doctors call it heat oedema, and for most people it is a nuisance rather than a warning. This piece covers why heat does it, how long it should last, the specific signs that mean it is not just the weather, and what genuinely helps. Sources are at the end.
The short answer
Your body sheds heat partly by widening the blood vessels near the skin, which brings warm blood to the surface where it can cool. That is exactly what you want it to do. The side effect is that widened vessels leak a little more fluid into the surrounding tissue, and gravity takes that fluid to the lowest available point — your ankles and feet.
Two other things pile on:
- Your calf pump is doing less. The lymphatic system that returns excess fluid has no pump of its own. It depends largely on the squeeze of surrounding muscle, particularly the calf. Hot weather makes people sit still more, not less, so the mechanism that clears the fluid is working less exactly when there is more of it to clear. We explain that in why your lymphatic system has no pump.
- Summer food is saltier. Crisps, barbecues, pub lunches, takeaways. Sodium and fluid retention travel together, and the NHS recommends adults have no more than 6g of salt a day (source 1).
Sitting in a garden chair for six hours on the hottest day of the year is, mechanically, not that different from a long-haul flight. Both remove the calf movement that shifts fluid; the heat just adds to it. We cover the travel version in swollen ankles after a flight.
How long it should last
Ordinary heat swelling is symmetrical — both ankles, roughly equally — painless, and it settles. A rough guide to what is unremarkable:
- Both feet and ankles, about the same on each side
- Puffy and tight, but not painful, and the skin looks normal in colour
- Noticeably better after a cool evening, a walk, and a night lying down
- Gone, or nearly gone, by the next morning
- Eases within a few days once the weather breaks
People who have just moved somewhere hot, or arrived on holiday, often find it settles on its own within a week or so as the body adjusts. If it is still there once the weather has cooled, it was probably not only the heat.
When it is not just the heat
Heat is a very convenient explanation, which is exactly why it is worth checking against the alternatives.
Get medical help urgently if:
- The swelling is in one leg only — heat affects both. One-sided swelling, especially with throbbing or cramping pain, or skin that is warm, red, darkened or discoloured, can be a sign of deep vein thrombosis (source 2)
- You are also breathless or have chest pain — call 999
Contact your GP if:
- The swelling does not settle overnight, or persists once the weather has cooled
- The skin is broken, hard, discoloured or leaking fluid
- You have a known heart, kidney, liver or thyroid condition and the swelling is new (source 3)
- You take medicines that can cause swelling — the NHS names some blood pressure medicines, contraceptive pills, hormone therapy, antidepressants and steroids (source 3). Do not stop a prescribed medicine; ask your GP or pharmacist to review it
Separately, heat itself can become dangerous. If someone is confused, has stopped sweating, has a very high temperature, or is not improving after 30 minutes of cooling, treat it as an emergency — that is heatstroke, not swollen ankles (source 4).
What actually helps in hot weather
Ranked honestly, most effective first.
- Move your calves, often. Twenty ankle circles and twenty heel raises every hour, even sitting in a deckchair. This is the single highest-value thing on the list, and it directly replaces the pump the heat has idled.
- Put your legs up. Ten minutes with your feet above heart level, ideally in the coolest room in the house. The fastest short-term relief available, and it costs nothing.
- Cool the skin. A cool shower, a cold flannel on the ankles, or feet in a basin of cool water. Cooling narrows the widened vessels that started the problem.
- Keep drinking normally. You lose more fluid in the heat, and drinking less does not reduce fluid retention. This is the most common mistake people make.
- Watch the salt. Summer eating is where most people quietly double their intake.
- Stay out of the strongest sun in the middle of the day, and keep rooms shaded and ventilated (source 5).
- Loosen everything. Tight sandal straps, socks with a hard elastic band and snug rings all make the same amount of fluid feel considerably worse.
- Compression socks are less pleasant in a heatwave but still work, particularly for travel days. Get them fitted properly, and check with a pharmacist or GP first if you have diabetes or a circulation condition.
These are the same levers that work year-round. We have ranked them by the effort each one asks in seven ways to support lymphatic flow, ranked.
What to avoid
- Water tablets you have not been prescribed. Diuretics are medicines for diagnosed conditions, and taking them in hot weather when you are already losing fluid is a particularly poor idea. The distinction is set out in water pills and herbal drops are not the same thing.
- Drinking less to "stop retaining". It does not work and it is riskier in the heat.
- A lot of alcohol in the sun. It adds to fluid loss and tends to arrive with salty food.
- Assuming it is the weather when it is one-sided. Heat is symmetrical. One leg is a different question.
Where a supplement fits, honestly
We make a herbal supplement, so it would be strange not to address it — and equally strange to overstate it.
There are no authorised GB health claims for the botanicals in this category in relation to lymphatic function or fluid balance, the research base for the claims often attached to these products is thin, and we are not going to tell you a supplement will stop your ankles swelling in a heatwave. We have written that out at length, with sources, in our honest look at whether lymphatic drainage supplements work.
What a daily supplement can realistically be is an anchor — a fixed ten-second moment the rest of a routine hangs off. If it is what makes the ankle circles and the ten minutes with your legs up actually happen on a hot week, that is a genuine and modest benefit, and it is the honest version of the claim. Havern Lymphatic Drainage Drops are nine botanicals plus vitamin C, every ingredient declared at 5.89% on the label, alcohol-free and made in the UK. Vitamin C contributes to the reduction of tiredness and fatigue and to normal collagen formation for the normal function of blood vessels. The tools for the outside half of the routine come together in the 180-Day Reset.
The short version
- Heat widens blood vessels to cool you down; fluid leaks out and gravity takes it to your ankles.
- Both sides, painless, settling overnight and easing when the weather breaks — ordinary.
- One leg only, painful, warm, red or discoloured is not the heat. Get help the same day.
- Calf movement, legs up and cooling the skin beat anything you can buy.
- Keep drinking normally. Do not take diuretics you have not been prescribed.
- A supplement is an anchor for the habit, not a mechanism.
Common questions
Why do my ankles swell in hot weather?
Because your body widens the blood vessels near the skin to shed heat, and those widened vessels leak slightly more fluid into the surrounding tissue. Gravity takes that fluid to the lowest point, your ankles and feet. Sitting still in the heat and eating saltier summer food both add to it. Doctors call this heat oedema.
Does heat cause swollen ankles?
Yes, directly. It is a recognised and common effect of warm weather, particularly in people who are less mobile, and particularly in the first days of a hot spell before the body adjusts. It normally affects both ankles equally and settles overnight.
How long does heat swelling last?
Usually it eases overnight and resolves within a few days of the weather cooling. People newly arrived somewhere hot often find it settles within a week or so as the body acclimatises. Swelling that persists after the heat has passed, or does not go down overnight, is worth a GP appointment.
How do I stop my feet swelling in hot weather?
Move your calves every hour with ankle circles and heel raises, spend ten minutes with your legs above heart level, cool the skin with a cool shower or a basin of cool water, keep drinking normally, cut added salt, stay out of the midday sun and loosen tight straps and socks. Do not restrict fluid and do not take diuretics you have not been prescribed.
Should I drink less water if my ankles are swollen in the heat?
No. Restricting fluid does not reduce fluid retention, and in hot weather you are already losing more through sweat, so drinking less increases the risk of dehydration. Reducing added salt is the useful dietary change.
Is it normal for only one ankle to swell in hot weather?
No. Heat affects both legs, so its swelling is symmetrical. Swelling in one leg only, especially with pain, warmth, redness or discoloured skin, can be a sign of a blood clot and needs urgent medical assessment rather than being put down to the weather.
References
- NHS. Salt in your diet. nhs.uk/live-well/eat-well/food-types/salt-in-your-diet
- NHS. DVT (deep vein thrombosis). nhs.uk/conditions/deep-vein-thrombosis-dvt
- NHS. Swollen ankles, feet and legs (oedema). nhs.uk/conditions/oedema
- NHS. Heat exhaustion and heatstroke. nhs.uk/conditions/heat-exhaustion-heatstroke
- GOV.UK. Heat: health effects and advice. gov.uk/government/collections/heat
For the full picture of why ankles swell at all, see why are my ankles swollen. Everything we have published is indexed on the lymphatic support guides page. This article is general information, not medical advice, and it does not replace an assessment by your GP or pharmacist.