Pustule: A pustule is a small collection of pus in the top layer of skin (epidermis) or beneath it in the dermis. Pustules frequently form in sweat glands or hair follicles. Pus is a mixture of inflammatory cells and liquid.
Put somewhat more simply, a pustule is a little pocket full of pus.
Quick GuideRosacea, Acne, Shingles: Common Adult Skin Diseases
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Last Editorial Review: 5/13/2016