Definition. Pustules are circumscribed, epidermic elevations usually of inflammatory origin, containing pus and varying in size from a pin-point to a finger-nail.
Pustules are similar to vesicles and to smaller blebs having an inflamed areola, except that the pustular contents are purulent instead of serous or seropurulent. Pustules may be primary but usually originate from vesicles or papules. Transitional forms are known as vesicopustules or papulopustules. Pustules vary in size from a pin-point as in small pustular eczema to that of a finger-nail as in impetigo and ecthyma. In shape they may be conic or round as in acne or furunculus, acuminate as in eczema and sycosis, flat as in impetigo, umbilicated as in variola and occasionally oblong or linear as in scabies. In color they may be yellowish or when they contain blood, red or brownish yellow. They may be surrounded by the normal-hued skin, or by an inflammatory areola; they may be indurated as in boils; or have an indurated base as in ecthyma. They may be situated around the sebaceous glands as in acne; around the hair- follicles as in sycosis; deep in the corium as in furuncles; or superficially seated as in eczema. The evolution of pustules is generally rapid; they usually rupture and form firm. yellowish, greenish or brownish crusts; or dry without rupture into somewhat lighter colored crusts. They are frequently attended with soreness or tenderness but rarely with any degree of itching. The largest number of pustules arise in the papillary layer; and, if the destructive process extend to several papillae or to the deeper parts of the skin, a scar may result. Epidermic pustules heal without cicatrix. The pathological process in variola is different from other pustulous affections, in that the exudation occurs within the cells instead of within a newly formed cavity. The distended cell-walls form a multilocular pock or pustule which cannot be opened by a single puncture.