Milaria

Other Names

Heat Rash
Miliaria
Lichen Tropicus
Prickly Heat
Eccrine miliaria
Milaria Rubra
Milaria Profunda
Milaria Crystallina

Background

This page refers to Miliaria, a self-limited condition commonly referred to as 'Heat Rash' or 'Prickly Heat'

History

Epidemiology

Prevalence
- Rubra seen in up to 4% of neonates^[1], 30% of all patients^[2]

Pathophysiology

Heat rash seen on the trunk^[3]

More heat rash seen on the trunk^[4]

General
- Self limited condition seen in athletes in hot, humid weather wearing tight fitting clothing
- Most commonly occurs under conditions of sweating

Etiology

General
- Acute inflammation of sweat ducts due to blockage of pores by macerated skin
- Ducts in the stratum corneum become dilated under pressure, rupture
- Often seen in areas of friction
- Subsequently, superficial vesicles in palpghian layer of skin
- Can progress to white papules (miliaria profunda) if duct ruptures a second times

Types

Milaria Rubra
- Most common form
Milaria Profunda
- Kertain plug develops in the obstructed poor, produces deeper vesicle within the dermis
- Occurs days to weeks after initial rash
Miliary Crystallina
- Sometimes called sudamina
- Common in neonates

Risk Factors

Environmental
- High Ambient Temperature
- High Humidity
- Lack of acclimitization to new environment
Activity/ Training
- Sustained physical exertion
- Intense exercise
- Occlusive clothing
Other
- Hyperhydrosis

Differential Diagnosis

Differential Diagnosis of Rash

Viral infection, specifically herpes or varicella
Bacterial infection, specifically folliculitis
Acne Vulgaris
Drug reaction
Viral exanthem
Allergic reaction
Cholinergic urticaria
Rhus dermatitis

Differential Diagnosis Heat Illness

Minor
Major

Miliaria Profunda seen in the popliteal fossa two weeks after the initial appearance of rash^[5]

Clinical Features

History
- Patients should describe a history of working or exercising in hot, humid conditions
- They often report intense pruritis
- Anhidrosis of affected areas
- Onset is typically rapid
Physical Exam^[6]
- Rash: pruritic, maculopapular, erythematous rash
- 2-4 mm papules or vesicles superimposed on an erythematous background
- In distribution of clothed areas of body
- Also common in waist or high sweaty or friction areas (neck, trunk, axilla, groin, waist)
- Note that folliculitis can present similarly
- Keratin plugs can develop days to weeks after initial rash (profunda stage)

Evaluation

Clinical diagnosis, no work up is required

Classification

Not applicable

Management

Mild cases
- Condition is self limiting and will resolve spontaneously
- Moving to cooler environment, removing constrictive clothing is often all that is needed
- Gentle exfoliation can help open obstructed pores
Moderate to Severe cases
- Distinguished by formation of pustules rather than vesicles
- Topical corticosteroids may help
  - E.g. Hydrocortisone cream BID for 7 days
- Topical or oral antibiotics should be considered if bacterial infection is suspected
Treating pruritis consider:
- Oral antihistamines
- Calamine Lotion
- Anhydrous lanolin
- Wet compresses
- Chlorhexadine
- Menthol-based
- Camphore- based
Prevention
- Wear light, loose-fitting clothing
- Avoid exercising in high heat or humid environments
- Exercise in air conditioned or cool climates
- Frequent cool showers or baths with mild soap

Rehab and Return to Play

Rehabilitation

Not specific rehabilitation guidelines

Return to Play/ Work

Self limited condition

Complications and Prognosis

Prognosis

Recurrence
- High likelihood of recurring
- Risk of recurrence decreases with acclimitization

Complications

Secondary Infection/ Folliculitis
- Typically seen with Staph or Strep

References

↑ Hidano, Akira, Ratna Purwoko, and Kumiko Jitsukawa. "Statistical survey of skin changes in Japanese neonates." Pediatric dermatology 3.2 (1986): 140-144.
↑ LYONS, ROBERT E., ROBERT LEVINE, and DAVID AULD. "Miliaria rubra: a manifestation of staphylococcal disease." Archives of Dermatology 86.3 (1962): 282-286.
↑ Image courtesy of sportsmedschool.com, "Heat Rash"
↑ Image courtesy of NHS.uk, "Heat Rash"
↑ Carter, Robert, Anisa M. Garcia, and Brian E. Souhan. "Patients presenting with miliaria while wearing flame resistant clothing in high ambient temperatures: a case series." Journal of Medical Case Reports 5.1 (2011): 1-4.
↑ Howe, Allyson S., and Barry P. Boden. "Heat-related illness in athletes." The American Journal of Sports Medicine 35.8 (2007): 1384-1395.

Created by:

John Kiel on 30 June 2019 22:48:01

Authors:

John Kiel

Last edited:

31 August 2022 15:03:13

Categories:

Environmental | Dermatology

[1] Hidano, Akira, Ratna Purwoko, and Kumiko Jitsukawa. "Statistical survey of skin changes in Japanese neonates." Pediatric dermatology 3.2 (1986): 140-144.

[2] LYONS, ROBERT E., ROBERT LEVINE, and DAVID AULD. "Miliaria rubra: a manifestation of staphylococcal disease." Archives of Dermatology 86.3 (1962): 282-286.

[3] Image courtesy of sportsmedschool.com, "Heat Rash"

[4] Image courtesy of NHS.uk, "Heat Rash"

[5] Carter, Robert, Anisa M. Garcia, and Brian E. Souhan. "Patients presenting with miliaria while wearing flame resistant clothing in high ambient temperatures: a case series." Journal of Medical Case Reports 5.1 (2011): 1-4.

[6] Howe, Allyson S., and Barry P. Boden. "Heat-related illness in athletes." The American Journal of Sports Medicine 35.8 (2007): 1384-1395.

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