About
A blister is a pocket of fluid protected by the overlying layer of skin. Blisters on the feet are usually caused by friction and can make wearing shoes and most activities painful. Blisters can also be caused by an insect bite, a skin burn, infection, sunburn, an allergic reaction or trauma.
Often, blisters on the feet result from wearing shoes that fit poorly. If the footwear is too tight or too loose, your feet can rub against the shoes causing friction. In this case, fluid will build up beneath the skin. Excessive moisture such as perspiration can also cause blisters, especially for runners in warm weather.