Aetiology

Miliaria crystallina represents the most superficial miliaria variant in which obstruction of the eccrine duct occurs in the stratum corneum.[1] Miliaria crystallina is most commonly seen in febrile diseases, situations in which occlusive clothing prevents dissipation of heat and moisture such as in bundled infants, after sunburn under hot and humid climatic conditions, in intensive care patients due to the medications used, and in newborns immediately after delivery in the setting of maternal fever.[1][3][6][7][9]​​[10]​ In addition, miliaria crystallina has been associated with underlying hypernatraemia both in adults and children.[12][13]

In miliaria rubra, obstruction of the eccrine duct occurs in the stratum malpighii of the epidermis.[1] Miliaria rubra occurs most commonly in hot and humid environments with use of occlusive clothing, affecting up to 30% of individuals with a maximal incidence after 2 to 5 months of exposure to a tropical environment.[14][15]

In miliaria profunda, obstruction of the eccrine duct occurs at the level of the dermo-epidermal junction following multiple episodes of miliaria rubra.[1] Miliaria profunda is usually only seen in tropical environments.[1]

Pathophysiology

The primary pathogenic process in miliaria is eccrine duct disruption.[16] Excessive sweating leads to over-hydration of the stratum corneum, which in turn leads to acrosyringeal occlusion.[17] However, sweating alone is not enough to produce duct disruption and miliaria. Elevated concentrations of sodium chloride on the skin, high humidity, and occlusive clothing may lead to eccrine duct disruption from maceration of the stratum corneum, and ultraviolet radiation-induced damage to epidermal cells may also cause ductal disruption.[16] There is also evidence that Staphylococcus epidermidis, which may be present in higher numbers on macerated, occluded skin, produces a polysaccharide substance that may obstruct the delivery of sweat to the skin.[18][19] Eccrine duct damage caused by high sodium content may lead to miliaria crystallina in the setting of hypernatraemia.[13]

Classification

Clinical classification[1]

Miliaria is classified according to the level at which the obstruction to the eccrine duct occurs:

Miliaria crystallina

  • Characterised by asymptomatic, fragile vesicles that appear in crops days to weeks after exposure to an inciting factor. Miliaria crystallina is the most superficial miliaria variant in which obstruction of the eccrine duct occurs in the stratum corneum.[1]

Miliaria rubra

  • 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] In miliaria rubra, obstruction of the eccrine duct occurs in the stratum malpighii of the epidermis.[1]

  • Miliaria rubra is characterised by erythematous non-follicular papules with a central vesicle at sites of friction and occlusion.[1][3]

Miliaria profunda

  • Usually seen in tropical environments after multiple episodes of miliaria rubra. Obstruction of the eccrine duct occurs at the level of the dermo-epidermal junction.[1] The variant is characterised by asymptomatic, flesh-coloured papules on the trunk and extremities with associated anhidrosis that can lead to hyperpyrexia and heat exhaustion.[1][4]

Use of this content is subject to our disclaimer