Miliaria results from obstruction of the sweat ducts caused by a combination of extreme heat and humidity. Depending on the level of obstruction of the sweat duct, different variants can be seen: miliaria crystallina (the most superficial form), miliaria rubra (commonly known as prickly heat), and miliaria profunda (the deepest form). Each type of miliaria is distinctive and readily recognizable clinically.

Miliaria crystallina lesions are clear mini vesicles approximately 1 mm in diameter that look like tiny drops of water on the skin. There are usually no symptoms associated with this superficial variant and it often goes unnoticed by the patient. The fragile nature of the tiny vesicles allows their ready rupture with bathing or friction.

Miliaria rubra, or prickly heat, is characterized tiny, red bumps that itch and sometimes burn. It is most common on the upper trunk and neck but can be seen anywhere on the skin except the face, palms and soles. Miliaria pustulosa is a variant of miliaria rubra that presents with pus bumps instead of red bumps. Bacterial infection can occur, especially when the itchy lesions are scratched.

Miliaria profunda lesions appear as white bumps 1 to 3 mm in diameter. Sweating prompts their appearance and they typically subside within 1 to 2 hours after sweating has stopped. There are usually no symptoms associated with this variant. It typically occurs on the trunk and extremities. There can be associated anhidrosis (loss of sweating) or compensatory hyperhidrosis (increased sweating). Bacterial infections are common.

Treatment of miliaria consists of seeking a cooler environment, wearing loose, breathable clothing, and drinking plenty of fluids. Topical and/or oral antibiotics should be used only where indicated for secondary infection. Corn starch or other light powders may help absorb moisture and minimize flares.

Lobitz WC, Dobson RL. Miliaria. Sweat retention syndrome. Pediatr Clin N Am 1996; 791-9.

Celeste Angel, D.O.
Department of Dermatology
Philadelphia College of Osteopathic Medicine/Frankford Hospital
Philadelphia, Pennsylvannia.