Miliaria is caused by blockage of the sweat ducts with subsequent leakage of eccrine sweat into the epidermis or dermis. It occurs in conditions of increased heat and humidity. There are three types of miliaria according to the level at which obstruction of the sweat duct occurs.
Miliaria crystallina: The ductal obstruction is most superficial, occurring in the stratum corneum. Clinically, this form of the disease produces tiny, fragile, clear vesicles.
Miliaria rubra: The obstruction occurs deeper within the epidermis and results in extremely pruritic erythematous papules.
Miliaria profunda: The ductal obstruction occurs at the dermal-epidermal junction. Sweat leaks into the papillary dermis and produces subtle asymptomatic flesh-colored papules.
Miliaria pustulosa: When pustules develop in lesions of miliaria rubra, the term miliaria pustulosa is used.