Miliaria is caused by occlusion of the epidermal portion of eccrine sweat ducts. There are 3 commonly recognized forms of miliaria that vary in symptoms, clinical presentation, and time course depending upon the level of occlusion: miliaria crystallina, miliaria rubra (prickly heat), and miliaria profunda (skin-colored papules with possible associated hypohidrosis or anhidrosis). Miliaria pustulosa is a pustular variant that may be seen in chronic cases of miliaria rubra.

Miliaria crystallina, also referred to as sudamina, is due to occlusion of the eccrine ducts at the superficial epidermis or stratum corneum. It may occur at any age but is common in neonates and infants, probably secondary to the immaturity and weakness of the duct structure. Clinically, it presents as largely asymptomatic 1- to 2-mm fragile vesicles. It has predilection for the face, neck, upper torso, and occluded areas. Fever, exposure to warm and humid environmental conditions, and occlusion (excessive clothing or swaddling) are predisposing factors.

Superficial occlusion is thought to result from increased hydration compounded with humidity and sweating. When the occlusion of the sweat duct is deeper in the epidermis, miliaria rubra (prickly heat), miliaria pustulosa, or miliaria profunda (skin-colored papules with possible associated hypohidrosis or anhidrosis) may result.