What Causes Blood Blisters?

A standard blister that appears on the skin is usually filled with a white-yellow liquid (pus). However, blisters can be filled with many different types of fluids that include serum, plasma, and even blood. A blood blister is any kind of raised skin with blood underneath it. Even though these blisters have an odd appearance to them that makes it seem like they are harmful, blood blisters don't usually cause health complications and should disappear completely within several weeks, which is true even if they don't obtain treatment for the blister. These blisters vary in size and are filled with a mixture of blood from a ruptured blood vessel and clear liquid.