Why does skin blister | how to treat skin blisters About blisters Blisters are small pockets of fluid that usually form in the upper layers of skin after it's been damaged. Blisters can develop anywhere on the body but are most common on the hands and feet. Fluid collects under the damaged skin, cushioning the tissue underneath. This protects the tissue from further damage and allows it to heal. Most blisters are filled with a clear fluid but may be filled with blood or pus if they become infla