History and exam

Key diagnostic factors

common

presence of risk factors

Key risk factors include profuse sweating, excessive heat and humidity, occlusive clothing, febrile illness, repeat episodes of miliaria rubra, and ultraviolet light exposure.

non-follicular vesicles and papules (all types)

Non-specific sign. However, all forms of miliaria are associated with non-follicular lesions as the disease involves the eccrine duct and not the hair follicle.[1]

asymptomatic eruption (crystallina)

The vesicular eruption of miliaria crystallina is asymptomatic.[1]

clear non-inflammatory vesicles (crystallina)

Miliaria crystallina is associated with clear non-inflammatory vesicles.[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@746c0e1​​

fragile vesicles (crystallina)

Miliaria crystallina is associated with fragile vesicles that often rupture with only slight friction and release a clear fluid.[1]

paroxysmal pruritus and stinging (rubra)

A key symptom in miliaria rubra is the presence of paroxysmal pruritus and pain exacerbated by stimuli that induce sweating.[1][2] Because of this symptom, miliaria rubra is often referred to as "prickly heat".

erythematous papulovesicles (rubra)

Non-specific sign. However, miliaria rubra is associated with erythema, unlike miliaria crystallina and miliaria profunda.[1][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@64bf0178

anhidrosis (profunda)

A key symptom in miliaria profunda is profound anhidrosis in the areas of involvement.[1] This can be severe enough to induce heat exhaustion, also referred to as tropical anhidrotic asthenia.[1][27] Miliaria rubra can also be associated with episodic anhidrosis in affected sites.[1][2] However, these episodes tend to be less severe than those associated with miliaria profunda.[1]

compensatory hyperhidrosis (profunda)

Miliaria profunda is often associated with compensatory hyper-hidrosis of the face, axillae, hands, and feet.[1]

flesh-coloured papules (profunda)

Non-specific sign. However, miliaria profunda is associated with deep-seated papules.[1]

Other diagnostic factors

common

desquamative healing (crystallina)

Miliaria crystallina resolves with "branny" desquamation.[1]

uncommon

weakness and malaise (profunda)

Heat exhaustion (tropical anhidrotic asthenia) in miliaria profunda is associated with weakness and malaise.

dyspnoea (profunda)

Heat exhaustion (tropical anhidrotic asthenia) in miliaria profunda is associated with dyspnoea.[1]

tachycardia (profunda)

Heat exhaustion (tropical anhidrotic asthenia) in miliaria profunda is associated with tachycardia.[1]

hyperpyrexia (profunda)

Heat exhaustion (tropical anhidrotic asthenia) in miliaria profunda is associated with hyperpyrexia.[1]

Risk factors

strong

profuse sweating

The primary pathogenic factor in all forms of miliaria is excessive sweating leading to over-hydration of the stratum corneum, in turn leading to acrosyringeal duct disruption.[16] In addition, excessive sweating increases the concentration of sodium chloride in the epidermis further leading to maceration of the stratum corneum and acrosyringeal duct disruption.[16]

Skin macerated by excessive sweating contains higher numbers of Staphylococcus epidermidis, which may contribute to the formation of miliaria through the production of a polysaccharide substance that may obstruct the acrosyringeal duct.[18][19]

Ubiquitous association with miliaria.

excessive heat and humidity

Profuse sweating induced by excessive heat and humidity leads to miliaria.

Ubiquitous association with miliaria.

occlusive clothing

Miliaria have been induced following application of occlusive pads and plastic wraps.[20][21]

Profuse sweating induced by occlusive clothing leads to miliaria.

Common association with miliaria in outdoor workers and bundled infants.

febrile illness

Profuse sweating induced by a febrile illness leads to miliaria.

Common association especially in hospitalised patients.

repeat episodes of miliaria rubra (for miliaria profunda)

Miliaria profunda is usually only produced after long lasting and/or multiple repeat episodes of miliaria rubra.[1][4]

Usually only seen in the tropics.[1][4]

Rare in neonates.[3]

ultraviolet light exposure

Sunburn plays a role in a sub-set of miliaria crystallina by inducing acrosyringeal duct disruption at the level of the stratum corneum.

Ultraviolet radiation epidermal cells are extruded and sandwiched between old and new corneocytes in the stratum corneum. These cells allow for dehiscence of the intra-corneal acrosyringeal duct and, if heavy sweating occurs, allows for the accumulation of sweat-forming miliaria.[16]

weak

neonatal age

Miliaria crystallina is seen in 4.5% of infants while miliaria rubra is seen in between 4% and 9% of infants.[5][11]

Mechanisms to explain the occurrence of miliaria crystallina in newborns include: a) the presence of immature sweat ducts during the first 2 weeks of life; b) maternal fever in select cases; c) moist occlusive environment created by amniotic fluid and vernix.[3][6]

cholinergic medicines

Eccrine glands are innervated by sympathetic fibres that release acetylcholine in order to cause sweating. Therefore, cholinergic medicines cause increased sweating and in some cases have been associated with the production of miliaria. Bethanechol, a cholinergic medicine that can induce sweating, has been associated with miliaria crystallina.[22]

isotretinoin

Alterations in the stratum corneum can result in acrosyringeal duct disruption and miliaria formation. Isotretinoin, a vitamin A derivative that alters the differentiation of keratinocytes, has been associated with the formation of miliaria crystallina.[23]

doxorubicin

Doxorubicin has been associated with miliaria crystallina.[24] It is thought that exfoliation, sloughing, and ulceration associated with the use of doxorubicin might create an environment conducive to developing miliaria crystallina.[24]

staphylococcal scalded skin syndrome

Miliaria crystallina has occurred following staphylococcal scalded skin syndrome.[25] It is postulated that staphylococcal toxins weakened the epidermis disrupting the acrosyringeal duct and creating a potential space for miliaria crystallina to form.[25]

atopic dermatitis

Miliaria rubra has been reported in patients with underlying atopic dermatitis. However, this association is weak as the individuals described in the case report were concurrently exposed to tropical heat and humid conditions while working in a mine in Australia.[26]

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