List the most common blistering diseases due to external agents. - Allergic contact dermatitis: Direct contact with allergens may cause an acute, pruritic vesicular eruption in the areas of contact. When it is due to plants such as poison ivy, the pattern is often linear, corresponding to areas where the the skin brushes the plant. The diagnosis can usually be made on the basis of history and clinical findings, particularly exposure to the offending agent. Skin biopsy for routine histologic examination may be helpful in difficult cases.
- Bullous drug eruptions: A number of drugs can produce characteristic vesiculobullous eruptions through toxic, immunologic, idiopathic, or phototoxic/photoallergic mechanisms.
- Miliaria crystallina: Superficial, fragile vesicles develop as eccrine sweat ducts become obstructed. Predisposing factors include high fever and occlusion, as well as sunburn. Clinical findings are usually diagnostic, but occasional cases require a skin biopsy.
- Blisters caused by physical agents: Heat, cold, chemicals, friction, pressure, and radiation (second-degree sunburn) may induce blisters. These can generally be identified readily by history and physical examination.
- Bullous arthropod bites: Small blisters around ankles, clothing constrictures, exposed skin areas, pet ownership, travel, or outdoor activities.
- Bullous impetigo: Fragile blisters, often ruptured with leading edge scale, with a positive culture for Staphylococcus or Streptococcus.
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