A blister is a small pocket of body fluid (lymph, serum, plasma, blood, or pus) within the upper layers of the skin, typically caused by forceful rubbing (friction), burning, freezing, chemical exposure or infection. Most blisters are filled with a clear fluid, either serum or plasma. However, blisters can be filled with blood (known as blood blisters) or with pus (for instance, if they become infected).Encyclopedia Entry for Blister :Blister Beetle.Latin name: Mylabris phalerata, Mylabris cichorii.Pinyin name: BAN MAO.Effect(s): To break blood and disperse concretion, attack toxin and cure sores.Plant part: dried body.