History
Miliaria crystallina
This form of miliaria usually affects neonates younger than 2 weeks and adults who are febrile or who recently moved to a tropical climate.
Lesions appear in crops within days to weeks of exposure to hot weather and disappear within hours to days. They are generally asymptomatic.
Miliaria rubra
This form usually affects neonates aged 1-3 weeks and adults who live in hot, humid environments.
Lesions may occur under transdermal medication patches. [2] They may develop within days of exposure to hot conditions, but they tend to appear after months of exposure. Lesions resolve within days after the patient is removed from the hot, humid environment.
Patients experience intense pruritus and stinging that is exacerbated by fever, heat, or exertion. They may report fatigue and heat intolerance, and they may notice decreased or absent sweating at the affected sites.
Miliaria profunda
This form occurs in individuals who usually live in a tropical climate and have had repeated episodes of miliaria rubra.
Lesions develop within minutes or hours after the stimulation of sweating. They resolve quickly, usually in less than 1 hour after the stimulus that causes sweating is removed. The lesions are asymptomatic.
Patients may report increased sweating in unaffected skin, swollen lymph nodes, hyperpyrexia, and symptoms of heat exhaustion (eg, dizziness, nausea, dyspnea, and palpitations).
Physical Examination
Miliaria crystallina
The characteristic lesions are clear superficial vesicles 1-2 mm in diameter. They occur in crops and are often confluent, without any surrounding erythema. In infants, lesions tend to occur on the head, neck, and upper part of the trunk; in adults, they occur on the trunk. The lesions rupture easily and resolve with superficial branny desquamation. (See the images below.)
Miliaria rubra
The characteristic lesions are uniform small erythematous papules and vesicular papules on a background of erythema (see the image below). They occur in a nonfollicular distribution and do not become confluent. In infants, lesions occur on the neck and in the groin and axillae. In adults, they occur on covered skin where friction is present (eg, neck, scalp, upper part of the trunk, and flexures). The face and volar areas are spared. Lesions may occur in erythematous patches resembling sunburn. [27] In late stages, anhidrosis is observed in affected skin.
When pustules develop in lesions of miliaria rubra, the term miliaria pustulosa is used. (See the images below.)
Miliaria profunda
The characteristic lesions are firm flesh-colored nonfollicular papules 1-3 mm in diameter. They occur primarily on the trunk but can also appear on the extremities. Lesions are transiently present after exertion or other stimulus that results in sweating. Affected skin shows diminished or absent sweating. In severe cases that lead to heat exhaustion, hyperpyrexia and tachycardia may be observed.
A rare giant centrifugal variant of miliaria profunda was described in a report on two infants (each aged ~3 mo) who presented with symmetrical asymptomatic lesions on the trunk and extensor extremities after a low-grade fever. [28] Unlike most forms of miliaria, the lesions in these children persisted for months. Another case report described this rare variant in association with congenital hypothyroidism. [29]
Complications
The most common complications of miliaria are secondary infection and heat intolerance. Secondary infection may appear as impetigo or as multiple discrete abscesses known as periporitis staphylogenes. Heat intolerance is most likely to develop in patients with miliaria profunda; it is recognized by anhidrosis of the affected skin, weakness, fatigue, dizziness, and even collapse. In its most severe form, this heat intolerance is known as tropical anhidrotic asthenia.
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Miliaria crystallina in infant. Note that lesions are confluent. Image from KE Greer, MD.
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Miliaria rubra in adult. Image from KE Greer, MD.
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Miliaria pustulosa. Image from KE Greer, MD.
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Miliaria crystallina. Note water-drop appearance of lesions. Image from KE Greer, MD.
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Miliaria crystallina in newborn child. Image from KE Greer, MD.
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Miliaria pustulosa. Image from KE Greer, MD.