Your fingers swell when walking in the heat primarily because your body is trying to cool itself down.
Here's a more detailed explanation:
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Thermoregulation: When you're exposed to heat, your body's thermoregulatory system kicks into high gear to maintain a stable internal temperature.
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Increased Blood Flow: One of the primary ways your body cools down is by increasing blood flow to the skin's surface. This allows heat to dissipate from the blood and radiate away from the body.
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Vasodilation: To accommodate the increased blood flow, blood vessels, including those in your hands and fingers, dilate (widen). This process is called vasodilation.
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Fluid Leakage: While vasodilation helps with cooling, it also causes fluid from the blood to leak into the surrounding tissues in your hands and fingers. This fluid accumulation is what leads to swelling.
In short, the increased blood flow necessary to cool you down in hot weather causes fluid to accumulate in the tissues of your fingers, leading to swelling. It's a normal physiological response, but can be uncomfortable.
