Blisters

Introduction

A blister is a pocket of fluid that forms between layers of skin, usually after repeated rubbing or pressure. Blisters commonly develop on the feet from poorly fitting shoes, long walks, hiking, running, or sports activities. They can also occur on the hands from tools or repetitive work. Anyone can develop a blister, but they are especially common in athletes, hikers, runners, and people wearing new or tight shoes. Risk factors include excessive friction, moisture (sweaty feet), heat, long periods of activity, poorly fitting footwear, and foot deformities such as bunions or hammertoes that create abnormal pressure points.

How Blisters Form

The skin is made up of several layers (Figure 1). The outer layer, called the epidermis, helps protect the body, while the deeper layer, called the dermis, contains blood vessels, nerves, and connective tissue. A blister forms when repeated friction or mechanical stress causes these skin layers to separate. The body then fills the space with fluid to protect the damaged area underneath. Most blisters contain a clear fluid called serum, but some may fill with blood if small blood vessels are injured, creating a blood blister. Friction, pressure, heat, and moisture all increase the risk of the skin layers separating and forming a blister.

Treatment of Blisters

Treatment for a blister depends on its size and severity. Small blisters that are not painful are often best left alone, since the overlying skin helps protect the area from infection. Larger or painful blisters may be carefully drained with a sterile needle while leaving the top layer of skin in place. The area should then be cleaned and covered with a protective bandage or blister pad. Reducing friction is very important, which may involve changing shoes, using moisture-wicking socks, applying padding, or modifying activities until the area heals. Most blisters heal within several days to two weeks if protected properly.

When to be Concerned about a Blister

Some blisters should be taken more seriously. Blisters that become increasingly red, swollen, warm, painful, or begin draining pus may be infected and should be evaluated by a healthcare professional. Blisters in patients with diabetes, poor circulation, or nerve damage are especially concerning because these individuals may not feel pain normally and may develop deeper skin breakdown underneath the blister. In diabetic patients, what appears to be a simple blister can sometimes be the early sign of a deeper foot ulcer, which can become infected and difficult to heal. Any blister in a diabetic patient that is large, persistent, draining, or associated with redness or swelling should be evaluated promptly.

Summary

Blisters are pockets of fluid that form when the skin is repeatedly rubbed or irritated. They are common on the feet from walking, running, or wearing tight shoes. Most blisters heal with rest, protection, and reducing friction. However, blisters that look infected or occur in people with diabetes should be checked by a doctor because they can sometimes lead to more serious problems.

Edited by Stephen Pinney MD, edited May 21st 2026.