Blisters: Definition, Causes & Treatment

Instructor: Artem Cheprasov
You've surely had a vesicle or bulla on your skin before. What's this? Well, you'll find out thanks to this lesson on the definition of a blister as well as the major causes of blisters and some of their potential treatment options.

Blisters: Definition

Think back to the last time you bought some new shoes. If you're like me, then it took you a while to break those shoes in. And one of the possible consequences of breaking in your shoes is a blister on your toe or heel. If you're unlucky, you'll get a lot of blisters!

Blister is the more common term for the dermatological terms of vesicle or bulla. A vesicle is a clearly demarcated and rounded elevation of thin skin that is filled with some sort of largely clear and watery fluid. A bulla is a vesicle that is greater than 0.5 cm in diameter.

This lesson goes over some of the many causes of blisters and some potential treatment options.


The types of blisters caused by those new shoes are known as friction blisters because the forces of friction cause them. In other words, the rubbing of the shoe over your skin. However, blisters can be caused by a lot of different problems.

For example, have you ever gotten so sick that you had a cold sore pop up on your lip? That cold sore was caused by the herpes virus. Unfortunately, the herpes virus forms some ugly looking blisters on your lip that begin to ooze fluid once they pop.

Other than infectious causes of blisters, blisters can also be caused by:

  • Thermal burns. Think: touching a really hot stove with your hands.
  • Frostbite, if you're into staying out in really cold weather a long time.
  • Contact dermatitis, or the inflammation of the skin as a result of your skin coming into contact with some sort of irritant. Think: poison ivy as you're hiking through the woods.
  • Allergic reactions, including reactions to drugs as well as environmental allergens.
  • Autoimmune disorders, such as bullous pemphigoid. An autoimmune disorders is one where your immune system attacks your own body.


Since there are so many potential causes of blisters, there is not one definite way of treating the blisters themselves. In many cases, the underlying cause of the blisters must be take care of and the blisters will heal on their own over time.

For example, if the blisters are caused by the herpes virus (a cold sore), then oral antiviral medication and/or topical creams may be given to help speed up the resolution of the blisters. If the blisters become secondarily infected with bacteria, antibiotics may need to be given as well.

With that in mind, some general ways by which blisters might be treated include:

  • Applying something like a bandaid or moleskin to help reduce the chance the blister(s) will get any worse.
  • Removing the liquid inside the blister to help with patient comfort. This is usually only practical for large blisters, or bullae. The fluid is carefully drained and the skin of the blister itself remains as intact as possible. This is important to help prevent infections.
  • If the blister has already popped then the use of antiseptics, topical antibiotic creams, and a sterile dressing would be appropriate.

Again, the points above are just general recommendations for the management of simple blisters caused by something like friction. They do not address the root cause of the blisters or more complex cases involving autoimmune disorders and the like. If the root cause isn't addressed then the blisters will keep coming back or will get worse.

Lesson Summary

A blister is another term for a vesicle or bulla. A vesicle is a clearly demarcated and rounded elevation of thin skin that is filled with some sort of largely clear and watery fluid. A bulla is a vesicle that is greater than 0.5 cm in diameter.

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