A blister is a collection of fluid between layers of the skin.  This is typically caused by injury or inflammation.  Injuries may be the result of mechanical trauma, heat injury, or chemical injury.  Most of us have had a blister from mechanical injury.  This often happens after buying a new pair of shoes that don't fit quite right.  Constant rubbing of the skin of the foot can separate the layers of the skin.  Blisters may also occur due to heat injury.  Many of us who have tried to cook understand this quite well!  A small splatter of boiling water on your hand will certainly get your attention!  Blisters can be caused by allergies (think "poison ivy") and all types of germs - including viruses, bacteria, fungi, and parasites.  So read more if you want to have the skinny on blisters!

What is a blister?

A blister is a collection of fluid between the layers of the skin.  This is typically the result of some sort of injury to the skin. 

What are the causes of blisters? 

Injury 

• Rubbing 
• A shearing force 
• Heat
• Chemicals
• Cold
• Electricity
• Ultraviolet rays from the su
• Radiation

Bleeding under the skin 

• This is sometimes called a "blood blister"
• The medical term would be "hematoma"

Infections 

• Viruses
• Bacteria
• Parasites
• Fungi  

Allergies

• Poison ivy 
• Insect bites 
• And many others  

How does a blister form?

Damaged skin and connective tissue cells separate from each other due to inflammation or injury.  Fluid drains from damaged cells and blood vessels and collects under the skin.  This fluid applies pressure that raises a blister.

Should I pop a blister?

No.  An un-popped blister still protects the body from infection.  A popped blister exposes the raw underlying skin to germs (especially bacteria).

How should a blister be treated?

Most blisters need little or no treatment when they have not ruptured.  A popped blister should be treated like an open sore or ulcer.  Topical antibiotic creams and ointments should be applied at least daily until the raw tissue heals.  All blisters should be protected from further injury.

When is a blister caused by an infection?

• Blisters on or near the mouth (without any known injury or chemical exposure) may be due to the cold sore virus (HSV).
• Blisters that are red and painful may be due to a bacterial skin infection. 

 Photo taken by Johannes Hemmerlein, 30 July 2006.

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