Approach

Characteristic history and examination findings are usually sufficient to diagnose miliaria.

History and symptoms

Miliaria crystallina is characterised by asymptomatic fragile vesicles that appear in crops days to weeks after exposure to an inciting factor.[1] Important factors that can induce miliaria crystallina include the following:[1][3][10][16][22][23][24]

  • Exposure to excessive heat and humidity, especially in tropical areas or during summer months in temperate areas

  • Use of occlusive clothing

  • Febrile illness

  • Following sunburn under hot and humid climatic conditions

  • Medicines such as isotretinoin, doxorubicin, or betacholine

  • Following staphylococcal scalded skin syndrome

  • Heavily bundled infants

  • In newborns immediately after delivery in the setting of maternal fever.

Miliaria rubra is characterised by an eruption of papules accompanied by a sensation of pruritus, prickling, burning, or tingling that is paroxysmal and exacerbated by stimuli that induce sweating.[1][2] Exacerbations of miliaria rubra are often followed by periods of anhidrosis in affected sites.[1][2] Miliaria rubra most commonly occurs in hot, humid environments, affecting up to 30% of people exposed to these conditions, and usually affects areas of friction and occlusion.[1][14][15] Although formation of miliaria rubra can occur as early as a few days after exposure to a tropical environment, it most commonly occurs after 2 to 5 months of continuous exposure to a hot and humid environment.[1][15]

Miliaria profunda typically occurs following repeated episodes of miliaria rubra in adults in the tropics and is characterised by asymptomatic lesions that become more prominent when the patient is stimulated to sweat.[1] In addition, patients are anhidrotic at sites of involvement, with compensatory hyper-hidrosis on the face, hands, and feet, and complain of weakness and dyspnoea from associated heat exhaustion.[1][27]

Physical examination

Miliaria crystallina is characterised by a diffuse eruption, typically on the trunk and proximal extremities, of translucent, fragile, non-follicular vesicles on a non-erythematous base. In neonates, the face and neck may also be involved.[3][5] If opened, the vesicles discharge a clear watery liquid. The eruption spontaneously resolves with a superficial branny desquamative appearance.[1] ("Branny" describes the similarity of the appearance to the hard outer layer of cereals.)

Miliaria rubra is characterised by erythematous, non-follicular papules with a central vesicle at sites of friction and occlusion.[1][3]In adults, the eruption occurs on the trunk with sparing of the face, while in neonates the face may be involved.[1][3][5] Non-follicular pustules can also form and, if widespread, the condition is termed miliaria pustulosa.[1] Anhidrosis may occur in affected sites.[1]

Miliaria profunda is characterised by flesh-coloured, non-folliculocentric, deep-seated papules concentrated on the trunk and proximal extremities with associated anhidrosis of affected areas.[1] Other findings include compensatory hyper-hidrosis of the face, axillae, hands, and feet as well as inguinal and axillary adenopathy.[1][Figure caption and citation for the preceding image starts]: Miliaria crystallina in hospitalised febrile patientFrom Brian L. Swick's collection, used with permission [Citation ends].com.bmj.content.model.Caption@40dcc495[Figure caption and citation for the preceding image starts]: Miliaria rubraFrom Brian L. Swick's collection, used with permission [Citation ends].com.bmj.content.model.Caption@6516d21b[Figure caption and citation for the preceding image starts]: Non-inflammatory fragile fluid filled blisters of miliaria crystallinaFrom Brian L. Swick's collection, used with permission [Citation ends].com.bmj.content.model.Caption@ee39a7f[Figure caption and citation for the preceding image starts]: Small tightly grouped inflammatory papules of miliaria rubraFrom Brian L. Swick's collection, used with permission [Citation ends].com.bmj.content.model.Caption@2105c8bb[Figure caption and citation for the preceding image starts]: Deep inflammatory papules of miliaria profundaFrom Brian L. Swick's collection, used with permission [Citation ends].com.bmj.content.model.Caption@10116061

Laboratory evaluation

Laboratory testing is typically not required as the diagnosis is usually made by historical and physical examination findings. However, a skin biopsy of an active lesion may be required for confirmation if the clinical presentation is less distinctive.

Haematoxylin- and eosin-stained sections from a lesion of miliaria crystallina demonstrate a sub-corneal vesicle situated over an acrosyringeal duct with no associated inflammatory infiltrate.

Haematoxylin- and eosin-stained sections from a lesion of miliaria rubra demonstrate spongiosis of an intra-epidermal sweat duct, sometimes forming a spongiotic vesicle, with lymphocytic exocytosis and a superficial perivascular infiltrate of lymphocytes and neutrophils.

Haematoxylin- and eosin-stained sections from a lesion of miliaria profunda demonstrates an intra-epidermal spongiotic vesicle associated with an acrosyringeal duct with lymphocytic exocytosis, and a superficial perivascular infiltrate of lymphocytes and neutrophils that is denser than that seen in miliaria rubra.

Herpetic infections can be ruled out using a Tzanck smear, viral direct fluorescent antibody, culture, or viral polymerase chain reaction (PCR). Staphylococcal infection can be ruled out with bacterial culture, and candidiasis infection can be ruled out using either a fungal culture or a potassium hydroxide (KOH) preparation.[Figure caption and citation for the preceding image starts]: Micrograph demonstrates the presence of herpes simplex virus in a Tzanck smearFrom Brian L. Swick's collection, used with permission [Citation ends].com.bmj.content.model.Caption@2380d35b

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