A blister is skin that has formed a raised bubble and is filled with fluid. Blisters can form anywhere on the skin in response to shoe rubbing or irritation.
The blisters are more likely to form in the back of the heel and sides of the foot. Often, the blisters are accompanied by discomfort or pain when they rub against shoes.
The most frequent cause of blisters is friction or pressure. Wearing shoes without socks, or wearing shoes too tight can lead to blistering. You can submit a blister on plants and toes if you are doing work that causes friction.