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 results from occlusion at the stratum corneum, while miliaria rubra occurs when the occlusion is deeper in the epidermis. In chronic cases of miliaria rubra, pustules may develop. This subtype of miliaria rubra is known as miliaria pustulosa. Chronic or recurrent miliaria rubra may also lead to miliaria profunda.

Miliaria profunda results from ductal occlusion at the dermal-epidermis junction or papillary dermis. Papules are larger than miliaria rubra and are firm and skin colored. The miliaria profunda eruption can be pruritic or asymptomatic. It usually is shorter lived than a miliaria rubra eruption (lasting usually no more than 1 hour after overheating has ceased). The most common locations for miliaria profunda are the extremities and trunk. Due to the blockage of the eccrine ducts, there is associated anhidrosis or hypohidrosis. This can be accompanied by a compensatory hyperhidrosis in the face and axilla. Usually, the patient does not complain of any symptoms, but the hypohidrosis can potentially lead to heat exhaustion manifesting as dizziness, fatigue, and weakness.

There is no racial or sex predisposition, but children and young infants have a greater risk for developing the disease due to immature eccrine ducts. Miliaria profunda is often seen in soldiers working in tropical climates.