Swollen ankles, tight shoes and a feeling of heaviness in the legs are common complaints during the warmer months. For some people, the swelling appears only after a long, hot day and improves overnight. For others, summer makes an existing circulation problem noticeably worse.
Heat can temporarily change the way blood and fluid move through the body, but it is not the only possible explanation for swollen legs. Persistent, painful or one-sided swelling may indicate an underlying condition and should not automatically be blamed on the weather.
What causes leg swelling in summer?
When the body is exposed to heat, blood vessels near the surface of the skin widen in a process known as vasodilation. This allows more warm blood to reach the skin, helping the body release heat into the surrounding environment.
Vasodilation is a normal and necessary part of temperature regulation. However, widening the blood vessels can also increase the amount of blood held in the lower limbs, particularly when a person remains standing or sitting for long periods. The resulting increase in pressure within the small blood vessels can encourage more fluid to move into the surrounding tissues.
Under normal circumstances, the venous and lymphatic systems help return this fluid to the circulation. When the amount of fluid entering the tissues temporarily exceeds the body’s ability to remove it, swelling, medically known as oedema or edema, can develop.
Why are the feet and ankles affected first?
Gravity plays an important role in summer leg swelling. When a person is upright, blood returning from the legs must travel against gravity to reach the heart. The contraction of the calf muscles during walking helps push this blood upwards, while valves inside the veins prevent it from flowing backwards.
If someone stands still, sits for several hours or moves very little, the calf muscle pump becomes less active. Blood and fluid are more likely to collect in the lowest parts of the body, which is why swelling usually becomes most visible around the feet, ankles and lower legs.
This type of dependent swelling may be more noticeable at the end of the day and improve after lying down or elevating the legs. Shoes can feel tighter, socks may leave deeper marks and the skin may appear stretched or shiny. In some cases, pressing the swollen area briefly leaves a temporary indentation, known as pitting oedema.
Heat can worsen an existing venous problem
Summer swelling does not always mean that a person has venous disease. Nevertheless, hot weather can make symptoms more noticeable in people whose leg veins already have difficulty returning blood efficiently to the heart.
Chronic venous insufficiency develops when the valves inside the veins become damaged or fail to close properly. Blood can then flow backwards and pool in the lower limbs, increasing pressure in the veins. In addition to swelling, symptoms may include aching, heaviness, fatigue, itching, cramps, visible spider veins or varicose veins and skin discolouration.
A 2023 observational study involving 1,683 patients with chronic venous insufficiency found that 56.6% reported worsening lower-limb oedema during warmer weather. The study does not prove that heat alone caused the swelling, and its results apply specifically to people already experiencing venous insufficiency. It does, however, support the common clinical observation that venous symptoms can become more noticeable in summer.
Who may be more likely to experience summer swelling?
Temporary leg swelling can affect otherwise healthy people, particularly after prolonged standing, long journeys or sudden exposure to a much warmer environment. The effect may be more pronounced when heat is combined with low physical activity.
People with chronic venous insufficiency, varicose veins, lymphatic disorders or limited mobility may find that their usual symptoms worsen during hot weather. Pregnancy, excess body weight and older age can also place additional strain on venous return.
Certain medicines may contribute to peripheral oedema, including some blood pressure medications, hormones, corticosteroids, anti-inflammatory medicines and other prescription drugs. A person who develops swelling after starting or changing medication should speak with a healthcare professional rather than stopping the treatment without medical advice.
Not every swollen leg is caused by the heat
Although hot weather is a possible trigger, leg swelling can have many different causes. These include injury, infection, pregnancy, high dietary sodium intake, chronic venous insufficiency, lymphoedema and side effects from medication.
Oedema may also be associated with conditions affecting the heart, kidneys, liver or thyroid. A deep vein thrombosis, which is a blood clot in a deep vein, can cause sudden swelling, usually in one leg. The appearance of swelling during summer does not rule out any of these conditions.
The pattern of symptoms can provide useful information, but it cannot establish a diagnosis on its own. Swelling that repeatedly returns, becomes progressively worse or occurs without an obvious reason requires medical evaluation.
What can help reduce mild leg swelling in hot weather?
When swelling is mild, affects both legs and is clearly associated with heat or prolonged standing, several simple measures may help. Gentle walking activates the calf muscles and supports the return of blood from the legs. Ankle movements, alternating between raising the heels and the toes, can also be useful when someone must remain seated.
Elevating the legs while resting can reduce the effect of gravity and help fluid move away from the ankles. Taking regular movement breaks, avoiding long periods in the same position and spending some time in a cooler environment may also relieve symptoms.
Comfortable shoes and clothing that do not constrict the ankles, calves or waist are preferable when swelling is present. Regular skin care is also important because persistently stretched or swollen skin can become dry, irritated and more vulnerable to injury or infection.
Hydration and salt: finding the right balance
Staying adequately hydrated is important in hot weather, particularly when fluid is being lost through sweating. However, drinking excessive amounts of water does not necessarily “flush out” oedema and may be inappropriate for people who have been advised to restrict fluids because of a heart or kidney condition.
A high sodium intake can encourage the body to retain more fluid and may make swelling worse in susceptible individuals. Reducing heavily salted and highly processed foods may therefore help, but severe dietary restrictions are not appropriate for everyone.
People with heart failure, kidney disease, liver disease or other conditions affecting fluid balance should follow the individual advice provided by their medical team rather than applying general hydration or sodium recommendations.
Should you wear compression stockings?
Graduated compression stockings can support venous return and may reduce aching and swelling in people with chronic venous disease. They apply controlled pressure to the lower leg, with the greatest pressure usually placed around the ankle.
Compression, however, is not suitable for every person or every cause of swelling. The correct size and level of pressure matter, while significant peripheral arterial disease and certain other medical conditions may make strong compression unsafe.
Anyone with unexplained, persistent or recurrent swelling should seek professional assessment before purchasing strong medical compression garments. Compression stockings should not be used as a substitute for diagnosing the cause of a newly swollen leg.
When does leg swelling require medical attention?
Mild swelling in both legs that appears after a hot day and improves with movement, cooling, elevation or overnight rest is generally less concerning. Medical advice is still appropriate if the swelling lasts for several days, keeps returning, becomes worse or is accompanied by skin changes, wounds or increasing discomfort.
Prompt medical evaluation is particularly important when swelling:
- develops suddenly or is severe;
- affects only one leg without a clear explanation;
- is accompanied by pain, tenderness, warmth, redness or skin discolouration;
- follows an injury and continues to worsen;
- occurs with fever, chills or signs of infection;
- appears in a person with known heart, kidney, liver or venous disease.
Sudden shortness of breath, chest pain, coughing up blood, a fast or irregular heartbeat, fainting or severe light-headedness may indicate a pulmonary embolism or another medical emergency. Emergency medical assistance should be sought immediately.
Understanding summer leg swelling
Leg swelling in summer is often the result of several factors acting together. Heat widens blood vessels, gravity encourages blood to collect in the lower limbs and prolonged sitting or standing reduces the action of the calf muscle pump. In many cases, the resulting swelling is temporary and improves with movement, cooling and elevation.
Nevertheless, heat should not become a convenient explanation for every swollen ankle. Summer can reveal or intensify symptoms of venous insufficiency, while persistent or unusual swelling may be associated with medication, lymphatic dysfunction, organ disease, infection or a blood clot.
Recognising the pattern, accompanying symptoms and warning signs can help distinguish a temporary response to hot weather from swelling that needs proper medical assessment.
