A blister forms when fluid collects under the superficial layer of skin, called the epidermis. Blood vessels leak fluid into the space under the epidermis when the skin is injured or irritated.

Common causes of skin blisters include:

• Friction injury
• Contact dermatitis:
• Poison ivy rash
• Burns:
• Second degree burns
• Drug reactions
• Impetigo
• Insect bites
• Jellyfish stings
• Frostbite
• Herpes simplex infections:
• Cold sores
• Genital herpes
• Chicken pox
• Shingles
• Herpetic whitlow
• Herpes gingivostomatitis
• Other viral infections:
• Herpangina
• Hand, foot, and mouth disease

Less common causes of skin blisters include:

• Stevens Johnson syndrome
• Erythema multiforme
• Epidermolysis bullosa
• Toxic epidermal necrolysis