Do Your Legs Swell in Extreme Heat?

Summer heat often brings swollen ankles and feet, especially after prolonged sitting, standing, or walking. Heat causes blood vessels to dilate, and gravity causes blood and fluid to pool in the lower parts of the body. As a result, shoes feel tight, sock marks remain on the skin, and ankles are noticeably thicker in the evening than in the morning.

According to the U.S. Centers for Disease Control and Prevention (CDC), this type of mild swelling is known as heat edema. It occurs in the first few days of exposure to high temperatures and usually resolves on its own. However, not all leg swelling should be attributed solely to the heat.

How to Recognize a Typical Reaction to Heat

Typical summer swelling is suggested when both ankles or feet are equally affected. The swelling is most pronounced in the evening after a day of standing or sitting, is not accompanied by severe pain, and the skin does not turn red or feel excessively warm to the touch. After elevating the legs and resting in a cool environment, the swelling usually subsides and may even disappear by morning.

The condition can be worsened by sitting for hours in a car or at a desk, standing still, consuming salty foods, and lack of physical activity. Additional contributing factors include excess body weight, pregnancy, varicose veins, and certain medications such as some blood pressure drugs, hormone therapy, corticosteroids, and certain antidepressants.

What You Can Do Yourself

For mild, bilateral swelling, a few simple measures can bring relief. During rest, it is helpful to prop your legs up on a pillow so they are above hip level, and every half hour to an hour, it is advisable to get up and take a short walk. Moving your feet up and down and rotating your ankles engages the calf muscles, which help pump blood back toward the heart.

Avoid prolonged standing in one spot, overly tight shoes, and socks that constrict the calf. Spending time in an air-conditioned room, rinsing your legs with lukewarm water, and staying well-hydrated can ease discomfort. You don't need to eliminate salt entirely without medical advice, but overly salty meals can increase fluid retention.

Do not take diuretics, or water pills, on your own. The CDC explicitly states that standard heat edema is not treated with diuretics because they can cause dehydration and interfere with the body's adaptation to heat. Patients already taking these medications for heart, kidney, or high blood pressure issues should not change their prescribed dose on their own.

Compression stockings can be helpful for venous insufficiency and prolonged standing, but they are not for everyone. People with poor arterial circulation, diabetes with sensory loss, skin infections, or severe heart disease should consult a doctor before using them. It is also crucial to choose the correct size and appropriate compression level.

When Swelling Requires Immediate Attention

Extra caution is needed when only one leg swells. Sudden swelling of one calf or the entire leg, especially if accompanied by pain or tenderness in the calf, warmer skin, and redness, can signal deep vein thrombosis (DVT). This is a blood clot in a deep vein that requires urgent medical evaluation. Although it cannot be confirmed or ruled out without examination and diagnostic tests, this condition most often affects only one side.

The risk of developing a clot is higher after long trips or periods of immobility, surgery, injury, hospitalization, during pregnancy and after childbirth, in people with a previous clot, and in some cancers and hormone therapies. However, a clot can sometimes develop without any obvious trigger.

If, along with a swollen and painful leg, you experience sudden shortness of breath, chest pain or pressure, rapid breathing, coughing up blood, extreme weakness, or loss of consciousness, call emergency services at 112 without delay. This cluster of symptoms may indicate that part of the clot has traveled to the lungs, causing a pulmonary embolism.

Other Serious Causes of Leg Swelling

A red, hot, painful, and rapidly growing swelling does not necessarily mean a clot. It could also be a bacterial infection of the skin and underlying tissue, especially if fever, chills, a wound, a crack between the toes, or a general feeling of being unwell are present. Cellulitis is treated with antibiotics and should not be managed solely with compresses and leg elevation.

A medical evaluation is also needed when swelling affects both legs but progressively worsens, does not subside after rest, or persists after the heat wave ends. Chronic swelling can be linked to chronic venous insufficiency, lymphedema, as well as heart, kidney, liver, or thyroid disease. The appearance of the swelling alone cannot reveal its cause.

In heart conditions, in addition to swollen legs, you may experience shortness of breath when walking or lying down, waking up feeling suffocated, unexplained fatigue, cough, sudden weight gain, or abdominal enlargement. Kidney problems may be indicated by swelling around the eyes, especially in the morning, changes in urine output, extremely foamy or dark urine, and swelling not limited to the ankles.

Pregnant women often experience mild, gradual ankle swelling, especially in the evening and on hot days. However, sudden increased swelling of the face, hands, or feet, severe headache, visual disturbances, pain under the ribs, nausea, or feeling extremely unwell can be signs of preeclampsia and require urgent contact with a doctor or maternity unit. People with diabetes should check their feet daily and not ignore swelling accompanied by redness, a wound, a blister, or loss of sensation.

Mild swelling of both ankles that occurs only in the evening during the hottest weather and disappears after rest is generally not a cause for alarm. However, swelling that comes on suddenly, affects only one leg, is painful, red, or warm to the touch is not a typical consequence of summer heat. The weather can explain some symptoms, but it should not become an excuse to ignore important warning signs.