Blisters form when the outer layers of skin are damaged, and fluid collects in the gap as a protective cushion while the skin heals. The most common cause is friction, but heat, cold, chemical exposure, infections, and some skin diseases can also trigger them.

Quick Scoop

Why it happens:

  • Rubbing or pressure makes layers of skin separate.
  • The body then fills that space with fluid to protect the tissue underneath.
  • Burns, frostbite, and chemical irritation can do the same thing.
  • Some conditions, like chickenpox, herpes, eczema, and autoimmune skin disorders, can also cause blistering.

Common examples:

  • Tight or poorly fitting shoes.
  • Repetitive hand use, like gardening or tool work.
  • Sunburn or a hot-surface burn.
  • Poison ivy or certain infections.

When to be careful

A blister is usually best left intact because the skin over it helps protect against infection. If a blister is very large, very painful, infected, or appears without an obvious cause, it is a good idea to get medical advice.

TL;DR: Blisters are basically the skin’s built-in cushion after damage, most often from friction.