Miliaria is a common disorder of the eccrine sweat glands that often occurs in conditions of increased heat and humidity. It is thought to be caused by blockage of the sweat ducts, which results in the leakage of eccrine sweat into the epidermis or dermis.[1]
Miliaria is classified into three main types according to the level at which obstruction of the sweat duct occurs, as follows:
Miliaria crystallina - Ductal obstruction is most superficial, occurring in the stratum corneum; clinically, this form of the disease produces tiny, fragile, clear vesicles (see the image below)
Miliaria rubra - Ductal obstruction occurs deeper within the epidermis and results in extremely pruritic erythematous papules; when pustules develop in lesions of miliaria rubra, the term miliaria pustulosa is used
Miliaria profunda - Ductal obstruction occurs at the dermal-epidermal junction; sweat leaks into the papillary dermis and produces subtle asymptomatic flesh-colored papules
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Miliaria crystallina in infant. Note that lesions are confluent. Image from KE Greer, MD.
Miliaria crystallina is asymptomatic and self-limited and therefore does not require treatment. However, miliaria rubra can cause great discomfort, and miliaria profunda may lead to heat exhaustion. Treatment of these conditions is warranted. (See Treatment.)
The primary stimuli for the development of miliaria are conditions of high heat and humidity that lead to excessive sweating. Occlusion of the skin due to clothing, bandages, transdermal medication patches,[2] or plastic sheets (in an experimental setting) can further contribute to pooling of sweat on the skin surface and overhydration of the stratum corneum. In susceptible persons, including infants, who have relatively immature eccrine glands, overhydration of the stratum corneum is thought to be sufficient to cause transient blockage of the acrosyringium. Foxc1 knockout in mice produces miliaria, suggesting that a genetic predisposition may exist.[3]
If hot humid conditions persist, the individual continues to produce excessive sweat but is unable to secrete the sweat onto the skin surface because of ductal blockage. This blockage results in the leakage of sweat en route to the skin surface, either in the dermis or epidermis, with relative anhidrosis.
When the point of leakage is in the stratum corneum or just below it, as in miliaria crystallina, little accompanying inflammation is present, and the lesions are asymptomatic. In contrast, in miliaria rubra, the leakage of sweat into the subcorneal layers produces spongiotic vesicles and a chronic periductal inflammatory cell infiltrate in the papillary dermis and lower epidermis. In miliaria profunda, the escape of sweat into the papillary dermis generates a substantial periductal lymphocytic infiltrate and spongiosis of the intraepidermal duct.
Resident skin bacteria (eg, Staphylococcus epidermidis and Staphylococcus aureus) are thought to play a role in the pathogenesis of miliaria, possibly through formation of biofilms.[4] Patients with miliaria have three times as many bacteria per unit area of skin as healthy control subjects do. Antimicrobial agents are effective in suppressing experimentally induced miliaria. Periodic acid-Schiff (PAS)-positive diastase-resistant material has been found in the intraductal plug that is consistent with staphylococcal extracellular polysaccharide substance (EPS). In an experimental study, only the strains of S epidermidis that produce EPS were able to induce miliaria.[5]
In late-stage miliaria, hyperkeratosis and parakeratosis of the acrosyringium are observed. A hyperkeratotic plug may appear to obstruct the eccrine duct, but this is believed to be a late change and not the precipitating cause of the sweat blockage.
The following causes of miliaria have been recognized:
Immaturity of the eccrine ducts - Neonates are thought to have immature eccrine ducts that easily rupture when sweating is induced; this rupture leads to miliaria
Occlusion of the skin, as with transdermal drug patches[2]
Occlusive clothing - A case series reported 18 cases of miliaria rubra in US Army personnel who routinely wore flame-resistant army combat uniforms composed of a 65% rayon/25% Kevlar/10% nylon blend while serving in the hot, arid conditions of Afghanistan[6]
Hot, humid conditions - Tropical climates, incubators in neonatal nurseries, and febrile illnesses may precipitate miliaria
Lack of acclimatization - Miliaria is common in individuals who move from a temperate climate to a tropical climate; it usually resolves after the individual has lived in the hot, humid conditions for many months
Exertion or high fever - Any stimulus to sweat may precipitate or exacerbate miliaria
Type I pseudohypoaldosteronism - This disorder of mineralocorticoid resistance leads to excessive loss of salt through eccrine secretions and is associated with repeated episodes of pustular miliaria rubra (miliaria pustulosa)[7, 8, 9]
Morvan syndrome - Miliaria rubra has been reported in this rare autoimmune disorder characterized by neuromyotonia, insomnia, hallucinations, pain, weight loss, and hyperhidrosis[10]
Drugs - Bethanechol, which promotes sweating, has been reported to cause miliaria, as have clonidine and neostigmine.[11] ; isotretinoin, which affects follicular differentiation, has also been reported to cause miliaria as well[12] ; miliaria crystallina has been reported after administration of doxorubicin[13, 14] and erythropoietin,[15] as well as idarubicin with retinoic acid[16]
Bacteria - Staphylococci are associated with miliaria, and antibiotics prevent miliaria in an experimental setting
Ultraviolet (UV) radiation - Some researchers have found that miliaria crystallina preferentially occurs in UV-exposed skin[17]
In the United States, miliaria crystallina is a common condition that occurs in neonates (peak age, 1 wk) and in individuals who are febrile or who have recently moved to a hot, humid climate. Miliaria rubra also is common in infants and adults who move to a tropical environment; this form occurs in as many as 30% of persons exposed to such conditions. Miliaria profunda is a rarer condition that occurs in only a minority of those who have repeated bouts of miliaria rubra.
Worldwide, miliaria is most common in tropical environments, especially among people who recently moved to such environments from more temperate zones. Miliaria has been a significant problem for American and European military personnel who serve in Southeast Asia and the Pacific.
A 1986 Japanese survey that included more than 5000 neonates revealed that miliaria crystallina was present in 4.5% (mean age, 1 wk) and that miliaria rubra was present in 4% (mean age, 11-14 d).[18] A 2006 survey study from Iran found a 1.3% incidence of miliaria in newborns.[19] A survey of pediatric patients in Northeastern India reported a 1.6% incidence of miliaria.[20] A hospital-based cross-sectional study of 150 patients presenting with sweat-induced dermatoses during the summer months in Puducherry, India, found that 84.1% had miliaria rubra, 4.6% had miliaria pustulosa, 3.3% had miliaria profunda, and 2.6% had miliaria crystallina.[21]
Age-, sex-, and race-related demographics
Miliaria crystallina and miliaria rubra can occur in persons of any age, but the diseases are most common in infants. A few cases of congenital miliaria crystallina have been reported.[22, 23] Miliaria profunda is more common in adults than in infants and children.
No sex predilection is recognized.
Miliaria occurs in individuals of all races, though some studies have found that Asians, who produce less sweat than Whites on average, are less likely to have miliaria rubra.
Most patients with miliaria recover uneventfully within a matter of weeks, once they move to a cooler environment. The main complications that may occur are altered heat regulation and secondary infection (see Complications).
Miliaria crystallina is generally an asymptomatic self-limited condition that resolves without complications over a period of days.[24] It may recur if hot, humid conditions persist.
Miliaria rubra also tends to resolve spontaneously when patients are moved to a cooler environment. Unlike patients with miliaria crystallina, however, those with miliaria rubra tend to be symptomatic, often reporting itching and stinging. Anhidrosis develops in the affected sites and may last weeks. If generalized, anhidrosis can lead to hyperpyrexia and heat exhaustion. Secondary infection is another possible complication of miliaria rubra; this is manifested as either impetigo or multiple discrete abscesses known as periporitis staphylogenes.
Miliaria profunda is itself a complication of repeated episodes of miliaria rubra. The lesions of miliaria profunda are asymptomatic, but compensatory facial and axillary hyperhidrosis may develop.[25] The widespread inability to sweat, the result of eccrine ductal rupture, is known as tropical anhidrotic asthenia; this condition predisposes patients to heat exhaustion during exertion in warm climates.
Some authors have suggested that subclinical miliaria is an initiating step in development of atopic dermatitis, on the grounds that histopathology showed PAS-positive material and bacteria present in the acrosyringium in cases of atopic dermatitis, whereas no blockage of eccrine ducts was seen in controls.[26]
Patients who have had miliaria, especially miliaria profunda, must be aware of the role of heat and humidity in precipitating this condition. These patients should be advised to wear lightweight clothing, stay out of the sun, avoid exertion in hot weather, and stay in an air-conditioned environment as much as possible.
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).
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.)
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Miliaria crystallina in infant. Note that lesions are confluent. Image from KE Greer, MD.
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Miliaria crystallina in newborn child. Image from KE Greer, MD.
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Miliaria crystallina. Note water-drop appearance of lesions. Image from KE Greer, MD.
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.
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Miliaria rubra in adult. Image from KE Greer, MD.
When pustules develop in lesions of miliaria rubra, the term miliaria pustulosa is used. (See the images below.)
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Miliaria pustulosa. Image from KE Greer, MD.
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Miliaria pustulosa. Image from KE Greer, MD.
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]
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.
Miliaria is clinically distinctive; therefore, few laboratory tests are necessary.
When miliaria rubra occurs in people with darker skin types, dermoscopy showing large white globules with surrounding darker halos, appearing like a “white bull's eye,” may be helpful in making the diagnosis.[30]
In miliaria crystallina, cytologic examination of the vesicular contents fails to reveal inflammatory cells or multinucleated giant cells (as would be expected in herpes vesicles).
In miliaria pustulosa, cytologic examination of the pustular contents reveals inflammatory cells. Unlike erythema toxicum neonatorum, eosinophils are not prominent. Gram staining may reveal gram-positive cocci (eg, staphylococci).
In miliaria crystallina, intracorneal or subcorneal vesicles communicate with eccrine sweat ducts, without surrounding inflammatory cells. Obstruction of the eccrine duct may be observed in the stratum corneum.
In miliaria rubra, spongiosis and spongiotic vesicles are observed in the stratum malpighii, in association with eccrine sweat ducts. Periductal inflammation is present.
In early miliaria profunda lesions, a predominantly lymphocytic periductal infiltrate is present in the papillary dermis and lower epidermis. A periodic acid-Schiff (PAS)-positive diastase-resistant eosinophilic cast may be seen in the ductal lumen. In later lesions, inflammatory cells may be present lower in the dermis, and lymphocytes may enter the eccrine duct. Spongiosis of the surrounding epidermis and parakeratotic hyperkeratosis of the acrosyringium may be observed.
In the granulomatous giant centrifugal variant of miliaria profunda, biopsies show mild spongiosis and acanthosis, hypergranulosis, and hyperplasia of the acrosyringia, the eccrine ducts, and infundibula, with invagination by keratin plugs. There is a granulomatous inflammatory infiltrate within the dermis, consisting of lymphocytes and foreign-body giant cells with a few neutrophils centered around the ruptured straight portion of the eccrine duct.[28]
Miliaria crystallina is asymptomatic and self-limited; accordingly, there is no compelling reason to treat it. However, miliaria rubra can cause great discomfort, and miliaria profunda may lead to heat exhaustion. Treatment of these conditions is warranted.
Prevention and treatment of miliaria consist primarily of controlling heat and humidity so that sweating is not stimulated. Measures may involve treating a febrile illness, removing occlusive clothing, limiting activity, providing air conditioning, or, as a last resort, having the patient move to a cooler climate.
Topical treatments that have been advocated involve lotions containing calamine, boric acid, or menthol; cool wet-to-dry compresses; frequent showering with soap (though some discourage excessive use of soap); topical corticosteroids; and topical antibiotics.
Topical application of anhydrous lanolin and isotretinoin has resulted in dramatic improvement in patients with miliaria profunda.[25]
Antimicrobial agents are effective in suppressing experimentally induced miliaria. Oral administration of antibiotics as prophylaxis for miliaria has been reported. Patients have also been treated with oral retinoids, vitamin A, and vitamin C, with variable success. To the authors' knowledge, no controlled trials have been conducted to demonstrate the effectiveness of any of these systemic therapies.
Because increased exertion leads to sweating, which greatly exacerbates miliaria, patients should be advised to limit their activity, especially in hot weather, until the miliaria resolves.
Patients with miliaria profunda are at particularly high risk for heat exhaustion during exertion in hot weather because their ability to dissipate heat by means of evaporation of sweat is impaired.
Patients should avoid exposure to conditions of high heat and humidity.
When patients are in tropical climates, they should wear lightweight clothing, avoid exertion, use sunscreen, and stay in air-conditioned buildings as much as possible.
In patients with a history of miliaria, the application of topical anhydrous lanolin before exercise may help prevent the formation of new lesions.
The goals of treating miliaria rubra and miliaria profunda are to provide symptomatic relief and to prevent hyperpyrexia and heat exhaustion. The author knows of no strong evidence indicating efficacy with systemic medications; therefore, topical medications are preferred. However, case reports of successful treatment of miliaria profunda with oral isotretinoin exist.
What is miliaria?What is the pathophysiology of miliaria?What causes miliaria?What is the prevalence of miliaria in the US?What is the global prevalence of miliaria?What are the racial predilections of miliaria?How does the prevalence of miliaria vary by sex?How does the incidence of miliaria vary by age?What is the prognosis of miliaria?What information about Miliaria should patients receive?Which clinical history findings are characteristic of miliaria crystallina?Which clinical history findings are characteristic of miliaria rubra?Which clinical history findings are characteristic of miliaria profunda?Which physical findings suggest miliaria crystallina?Which physical findings suggest miliaria rubra?Which physical findings suggest miliaria profunda?What are complications of miliaria?How is miliaria differentiated from other cutaneous eruptions?What are the differential diagnoses for Miliaria?What is the role of lab studies in the diagnosis of miliaria?Which imaging studies are performed in the diagnosis of miliaria?Which histologic findings suggest miliaria?What are the treatment options for miliaria?Which activity modifications are used in the treatment of miliaria?How is miliaria prevented?Which medications are used in the treatment of miliaria?Which medications in the drug class Emollients are used in the treatment of Miliaria?
Nikki A Levin, MD, PhD, Associate Professor of Medicine, Division of Dermatology, University of Massachusetts Medical School
Disclosure: Nothing to disclose.
Specialty Editors
Michael J Wells, MD, FAAD, Dermatologic/Mohs Surgeon, The Surgery Center at Plano Dermatology
Disclosure: Nothing to disclose.
Rosalie Elenitsas, MD, Herman Beerman Professor of Dermatology, University of Pennsylvania School of Medicine; Director, Penn Cutaneous Pathology Services, Department of Dermatology, University of Pennsylvania Health System
Disclosure: Received royalty from Lippincott Williams Wilkins for textbook editor.
Chief Editor
Dirk M Elston, MD, Professor and Chairman, Department of Dermatology and Dermatologic Surgery, Medical University of South Carolina College of Medicine
Disclosure: Nothing to disclose.
Additional Contributors
Janet Fairley, MD, Professor and Head, Department of Dermatology, University of Iowa, Roy J and Lucille A Carver College of Medicine
Disclosure: Nothing to disclose.
References
Disorders of the sweat glands. Griffiths C, Barker J, Bleiker T, Hussain W, Simpson R, eds. Rook's Textbook of Dermatology. 10th ed. Hoboken, NJ: Wiley-Blackwell; 2024. Chap 92.
Kumar S, Mahajan BB, Kaur S, Singh A. Erythropoietin induced miliaria crystallina: A possible new adverse effect of erythropoietin. Int J Case Rep Images. 2014. 5 (9):634-7.
Huda M, Saha P. Pattern of dermatosis among pediatric patients attending a medical college hospital in northeastern region of India. Indian J Dermatol. 2009. 49:189.
Al-Hilo, Maytham M, Al-Saedy SJ, Alwan AI. Atypical Presentation of Miliaria in Iraqi Patients Attending Al-Kindy Teaching Hospital in Baghdad: A Clinical Descriptive Study. Am J Dermatol Venereol. 2012. 41-6.
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