blister

A blister is a small pocket of fluid that forms between layers of the skin after injury. It is usually filled with clear serum and is most commonly seen on the feet or hands from friction, but can also result from burns, chemical exposure, frostbite, or other skin-damaging processes. Blisters can occur in people with certain medical conditions that affect the skin, though most are due to local trauma.

Common causes include rubbing from ill-fitting footwear or repetitive motion, thermal or chemical burns, radiation, and frostbite. The fluid-filled space helps protect damaged tissue and facilitates healing while the skin beneath remains intact.

Pathophysiology involves disruption of the connections between skin layers or damage to local capillaries, allowing fluid to collect between the epidermis and dermis. The resulting vesicle (small) or bulla (larger) is typically tender.

Symptoms and diagnosis are usually straightforward: a raised, dome-shaped, fluid-filled lesion on the skin, often painful. The fluid is typically clear; color changes may occur if blood or pus is present. Diagnosis is clinical; additional testing is rare unless infection is suspected or an unusual presentation suggests another condition.

Treatment focuses on protection and infection prevention. Keep the blister clean and dry, and cover with a clean, nonstick dressing. If the blister is large, a clinician may drain it using sterile technique while leaving the overlying skin intact. Do not pop blisters that are infected or on the face in children. Seek medical care for signs of infection or extensive burns. Prevention includes proper footwear, padding, and managing friction. Most blisters heal within one to two weeks without scarring.