When should you see a doctor about skin blisters?

A blister is a pocket of fluid beneath or within the skin. Friction and sunburn can affect exposed or rubbed areas. Contact dermatitis may appear where an irritant or allergen touched the skin, while dyshidrotic eczema often causes small itchy blisters on the hands or feet. Cold sores cluster around the lips, and shingles usually causes a painful, one-sided band of blisters. Recurrent widespread blisters can have an immune-related cause such as bullous pemphigoid.

Wash gently, pat dry, and cover the blister with a clean non-stick dressing. Avoid deliberately bursting it, peeling loose skin, or applying household remedies. Reduce rubbing and keep hands clean before touching the area. Record the onset, location, pain or itch, recent products, sun exposure, illness, and medicines. Antiviral treatment may help selected infections, but it works best when prescribed for the correct cause.

Seek same-day care for rapidly spreading blisters, severe pain, pus, increasing warmth, red streaks, fever, or blisters near the eyes. Go to emergency care for breathing difficulty, facial swelling, confusion, skin peeling, or sores involving the mouth, eyes, or genitals. People with diabetes, reduced immunity, or extensive burns should obtain advice early. A clinician may need to swab, test, or sample the skin rather than treating the appearance alone.

Could this be infectious, allergic, or immune-related? Should the blister be covered or tested? Which symptoms mean I need emergency care, and can I safely use an antiviral or pain medicine with my current medicines?