Five Common Causes of Blisters

A blister is a small, fluid-filled bubble on the skin that can happen for several reasons -- including friction, trauma, or infection.  Here are five of the most common reasons why this skin condition occurs.

Second-Degree Burns

Burns are separated into three categories: first degree, second degree, or third degree.  A first-degree burn is a superficial heat injury that causes the skin to turn red and appear like a sunburn. A second-degree burn is a partial-thickness heat injury that causes the skin to turn red and blister. A third-degree burn is a full-thickness skin injury that causes the skin to turn white or black. 

Second-degree burns are one of the most common causes of skin blistering. It’s important to note that if you do sustain a burn that creates a blister, it’s best not to “pop” the blister because doing so can create an opening for bacteria to enter the skin and cause an infection.


A friction blister happens when there is frequent rubbing or pressure against the skin that causes the outermost layer of skin to separate from the other layers.  Then the gap between these layers of skin fills with fluid or, if the friction is significant enough, with blood.  The most common location for friction blisters is on the feet since tight or ill-fitting shoes worn for extended periods of time can irritate the skin on the heels and toes.  As with second-degree burn blisters, it’s best not to try to “pop” friction blisters, since that can increase the likelihood of infection.


Shingles is a viral infection caused by the Varicella-Zoster virus (VZV).   The virus usually starts as a burning sensation along a single nerve pathway, which is called a “dermatome.”  Then small red bumps appear, which evolve into a line of small, painful blisters called “vesicles.” 

It’s important to seek prompt medical care if you develop these blisters since antiviral medications that treat shingles are most effective if they’re begun within the first 48 hours of symptoms.


The Herpes Simplex virus (HSV) is categorized into HSV 1 and HSV 2.  The virus causes clusters of small blisters called “vesicles” to form on the mouth, which is known as oral herpes, or “cold sores.”  It can also cause vesicles to appear on the genitals, which is known as genital herpes.  HSV 1 used to be responsible for more than 80% of cold sores, and HSV 2 used to be responsible for more than 80% of genital herpes infections.  However, largely due to oral sex, that distinction no longer exists, which means cold sores can be caused by HSV 2, and genital herpes can be caused by HSV 1. 

There is currently no accurate blood test for HSV.  If you develop blisters around your lips or genitals, a health care provider can take a sample of the fluid in the blister and do a viral culture, which can accurately determine if the blisters are caused by HSV and whether the infection is HSV 1 or HSV 2.  Antiviral medications can also cause HSV outbreaks to resolve sooner.

Chicken Pox

Chickenpox is a viral infection caused by the Varicella-Zoster Virus (VZV), the same virus that causes shingles.  In addition to fever, headaches, and fatigue, varicella causes a diffuse outbreak of small, itchy blisters.  While the varicella vaccine has caused a dramatic decrease in varicella infections, people who have not received the varicella vaccine or have weakened immune systems can still contract the virus. 

If you or someone you know develop symptoms of chickenpox, it’s important to be isolated from other people, since the varicella virus is airborne, and therefore highly contagious.


Written by Sarah Thebarge, Physician Assistant