Blisters are fluid filled sacs which develop beneath the surface layer of the skin. They are usually caused by friction or extremes of temperature such as a scald or a freeze. There are also some dermatological reasons why some people develop blisters such as infection.
Blisters can be subdivided into categories such as bullae, vesicles, or pustules .
Bullae are large blister sites filled with following excessive skin trauma.
Vesicles are small blisters which often appear in clusters and usually indicate a dermatological problem or infection such as tinea pedis (athletes foot).
Pustules are pus filled blisters which may be associated with specific conditions such as psoriasis / palmoplantar pustulosis.