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Miliaria crystallina, also known as sudamina, is the mildest form of heat rash and is characterized by small, fairly fragile, fluid filled blisters. It is caused by blocked sweat glands which force the backed-up sweat to flow into the epidermis and erupt as blisters. This condition is prevented by allowing sweat to evaporate and by avoiding conditions that overheat the skin.
Many conditions can lead to blocked sweat glands and cause miliaria crystallina. Tropical climates with high heat and humidity as well as excessive exercise in hot weather can tax the sweat glands by reducing skin evaporation, leading to blockage of the pores and backing up of the sweat into the superficial layers of the skin. Some fabrics, heavy creams, and sun screens can prevent the natural evaporation of sweat, causing the sweat glands to become clogged.
Sudamina is a side effect of the prescription medications bethanechol, clonidine, isotretinoin, and doxorubicin. In addition, people confined to bed rest with restricted movement can develop this form of heat rash when the skin is covered and excessive sweat is not allowed to evaporate. This condition is also common in newborn babies who are often wrapped tightly, even in the summer or while in an incubator, and have sweat glands that have not completely matured.
Miliaria crystallina boils can ripen anywhere on the body. The most common places for these boils are where the skin holds heat and sweat, such as skin folds, or where clothing wears on the skin. On babies, the sudamina blisters most often develop in or near the underarms, around the groin, or along the neck.
The best treatment for miliaria crystallina is to prevent it by curtailing sweating and allowing the skin to breath and the sweat to evaporate. This means not exercising excessively in hot weather, wearing appropriate clothing in hot weather, and taking advantage of air conditioning when the weather is hot and humid. Heavy creams should be avoided when the weather is hot and humid to allow the sweat to be released and to promote better evaporation from the skin.
If miliaria crystallina develops, it can be treated and relieved with cold compresses. If this does not work, calamine lotion will often be sufficient to provide comfort. In more severe cases, topical steroids may be required. If the blisters break and become infected, a topical antibiotic ointment may be needed.
Heat rash, clinically known as miliaria, comes in four degrees of increasing severity. Miliaria crystallina is the most benign form of heat rash, miliaria rubra and miliaria profunda are the intermediate forms, and miliaria pustulosa is the most severe. Each form of miliaria is characterized by more severe blockage of the sweat glands and results in greater skin damage and longer recovery time.