Your ankles can swell when it is hot outside primarily due to a condition called heat edema, which is a type of swelling caused by the body’s response to heat. When the temperature rises, your blood vessels, especially those near the skin, dilate (expand) to help release heat and cool your body down. This dilation causes more blood to pool in the lower extremities, such as your ankles and feet, because gravity pulls the fluid downward. The increased blood flow and vessel dilation lead to fluid leaking from the blood vessels into the surrounding tissues, causing swelling[1].
Heat edema is generally harmless and temporary, often resolving once you cool down or elevate your legs. However, it is important to understand the underlying mechanisms and other possible causes of ankle swelling in hot weather to distinguish normal heat-related swelling from more serious medical conditions.
When it is hot, your body tries to maintain a stable internal temperature through a process called thermoregulation. One key part of this process is vasodilation, where blood vessels widen to increase blood flow to the skin, allowing heat to escape. This increased blood flow can overwhelm the veins in your legs, which are responsible for returning blood to the heart. Veins have one-way valves that prevent blood from flowing backward, but in some people, these valves may weaken or become damaged, a condition known as chronic venous insufficiency. When this happens, blood pools in the lower legs, increasing pressure in the veins (venous hypertension), which forces fluid out of the vessels and into the surrounding tissues, causing swelling[2].
In addition to venous issues, the lymphatic system, which helps drain excess fluid from tissues, can become overwhelmed if too much fluid accumulates. This can lead to lymphoedema, a chronic swelling condition. While heat edema is usually temporary and mild, chronic swelling due to venous or lymphatic problems requires medical attention[2].
Other factors that can contribute to ankle swelling in hot weather include:
– Prolonged standing or sitting without moving, which reduces the muscle pump action that helps push blood back to the heart.
– Certain medications, such as calcium channel blockers used for high blood pressure, which can cause fluid retention and swelling.
– Underlying medical conditions like heart failure, kidney disease, or liver disease, which impair the body’s ability to manage fluid balance and can cause pitting edema, a type of swelling where pressing on the skin leaves a temporary indentation[6].
Heat edema is part of a broader category of heat-related illnesses, which range from mild conditions like heat cramps and heat rash to severe ones like heat stroke. Heat edema specifically refers to swelling of the extremities due to water retention following blood vessel dilation in response to heat[1].
It is important to differentiate heat edema from other causes of swollen ankles that may require urgent medical care. For example, cellulitis is a bacterial skin infection that causes redness, warmth, swelling, and pain, usually in one leg, and needs prompt treatment[4]. Another serious condition is acute Charcot arthropathy, often seen in people with diabetes, which causes a red, hot, swollen foot or ankle due to inflammation and bone damage[5].
In people with autoimmune diseases like lupus, heat and sun exposure can trigger inflammation and swelling, sometimes causing hot, swollen areas on the body including the feet and ankles[3][7]. Photosensitivity in lupus leads to skin damage and immune system activation, which can worsen swelling and discomfort.
To reduce ankle swelling in hot weather, it is helpful to:
– Elevate your legs when resting to help fluid return to the heart.
– Stay hydrated to support healthy circulation.
– Avoid prolonged standing or sitting; move around regularly to activate the calf muscles.
– Wear compression stockings if recommended by a healthcare provider to improve venous return.
– Avoid excessive salt intake, which can increase fluid retention.
If swelling is severe, persistent, painful, or accompanied by other symptoms such as shortness of breath, chest pain, redness, or warmth in the leg, it is important to seek medical evaluation to rule out serious conditions like deep vein thrombosis, heart failure, or infection.
In summary, your ankles swell when it is hot outside mainly because heat causes blood vessels to dilate, increasing blood pooling and fluid leakage into tissues, a condition known as heat edema. This is usually temporary and harmless but can be worsened by venous insufficiency, lymphatic problems, medications, or underlying diseases. Proper care and awareness of warning signs are essential to manage swelling effectively.
Sources:
[1] Heat illness – Wikipedia
[2] Causes & Treatment – Lymphoedema / Oedema of Legs & Feet – Legs Matter
[3] 5 Reasons You Have Random Hot Spots on Your Body – MyLupusTeam
[4] Signs & Symptoms – Cellulitis a Skin Infection of the Legs & Feet – Legs Matter
[5] Pathogenesis of Acute Diabetic Charcot Arthropathy in the Foot and Ankle – Orthopedic Reviews
[6] Pitting Edema vs. Lymphedema: How to Tell Them Apart – Norton School
[7] Lupus and the Feet – Lupus Foundation of America
