Three forms of miliaria occur, but only the common form will be discussed here. Under favorable conditions, anyone can develop miliaria. Infants and young children, however, seem particularly prone to this eruption caused by sweat-duct occlusion. The onset may be gradual or sudden and usually suggests an acute viral exanthem. Infants become cranky and irritable, while those able to verbalize complain of an intense pricking discomfort rather than pruritus.
Sheets of tightly grouped geometrically distributed irritable red papules develop; these wax and wane in intensity depending on the ambient temperature and degree of activity. Because the sweat duct is temporarily blocked and the gland will continue to secrete, any sweat stimulus will cause a sudden apparent exacerbation. This can happen even after clinical resolution while the ducts are still recovering patency. In infants, crying, emotional distress, and exertion associated with feeding frequently cause shortlived flares.
Individual lesions may wax and wane but usually regress once the precipitating factors are removed. An exception is when secondary infection supervenes. Then the lesions may become pustular or develop into a frank impetigo.
An immature sweat gland apparatus in infants and individual genetic susceptibility play a role. Rapid change in ambient temperature, high humidity, occlusive clothing, friction from garments, and any factor that favors skin surface bacterial colonization predisposes to miliaria. A recent study implicates certain strains of S. epidermidis as the source of the polysaccharide plug that can be demonstrated microscopically in the eccrine duct orifice. Once occlusion has occurred, any stimulus that initiates sweating will cause a short-lived exacerbation.
Self-treatment is not a problem in miliaria.
Time of onset in relation to weather changes, heat stress, febrile illness, and other provoking factors will usually identify the reason for occurrence.
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