<Tr> <Th> MeSH </Th> <Td> D001768 </Td> </Tr> <Tr> <Td_colspan="2"> (edit on Wikidata) </Td> </Tr> <P> 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 (if they become infected). </P> <P> The word "blister" entered English in the 14th century . It came from the Middle Dutch "bluyster" and was a modification of the Old French "blostre", which meant a leprous nodule--a rise in the skin due to leprosy . In dermatology today, the words vesicle and bulla refer to blisters of smaller or greater size, respectively . </P>

What's the fluid that comes out of blisters