Miliaria

What is miliaria?

Miliaria is a common skin disease caused by blockage and/or inflammation of eccrine sweat ducts.  Miliaria is frequently seen in hot, humid or tropical climates, in patients in hospital, and in the neonatal period. Miliaria is also known as sweat rash.

Based on the level of the sweat duct obstruction, miliaria is divided into three subtypes:

• Miliaria crystallina (sudamina), caused by obstruction of the sweat ducts close to the surface of the skin (epidermis);
• Miliaria rubra, caused by obstruction of the sweat ducts deeper in the epidermis;
• Miliaria profunda (tropical anhidrosis), the result of sweat leaking into the middle layer of skin (dermis).

Who gets miliaria?

• Miliaria crystallina is most commonly seen in neonates with the mean age of 1 week, affecting up to 9% of all neonates. It can also occur in adults with fever.
• Miliaria rubra is the most common form of miliaria. It is seen in children and in up to 30% of adults who move to a tropical environment or are unexpectedly exposed to heat and humidity.
• Miliaria profunda is rare and presents in adult males. It is a complication of repeated episodes of miliaria rubra.

What causes miliaria?

Miliaria results from sweating. The main contributing causes are:

• Immature sweat ducts in a newborn child
• A hot and humid environment
• Intense physical activity
• Fever
• Occlusion of the skin with non-porous dressings or synthetic clothing against the skin
• Prolonged bed rest.

Other diseases and treatments that have been associated with miliaria are:

• Drug-induced hyperhidrosis
• Adverse reaction to medication (isotretinoin, doxorubicin)
• Stevens-Johnson syndrome / toxic epidermal necrolysis
• Genetic disease (Morvan syndrome and pseudohypoaldosteronism type I)
• Radiotherapy

What are the clinical features of miliaria? 

• Miliaria crystallina appears as 1–2 mm superficial clear blisters that easily break. The blisters can look like beads of sweat. There is no inflammation. The blisters are usually seen widely spread on the head, neck, and upper trunk.
• Miliaria rubra is the most common type of miliaria results in red, 2–4 mm, non-follicular papules and papulovesicles. They are very itchy. Background erythema is often present. In children, miliaria affects the skin folds of the neck, axilla or groin. In adults, miliaria often affects the upper trunk, scalp, neck and flexures, particularly areas of friction with clothing.
• Miliaria pustulosa is a variant of milia rubra in which there are pustules.
• Miliaria profunda describes asymptomatic deep papules. The flesh–coloured, 1–3 mm diameter papules usually arise on the trunk and extremities.

What are the complications of miliaria?

The complications of miliaria include:

• Secondary bacterial infection, most commonly caused by staphylococci
• Impaired thermoregulation
• Hyperhidrosis in non-affected areas.

How is miliaria diagnosed?

Miliaria is diagnosed by its typical clinical presentation. In severe cases or repeated episodes, punch biopsy can be useful.

What is the differential diagnosis for miliaria?

Skin disorders that present with papules, vesicles or pustules that look similar to miliaria, include:

• Herpes simplex
• Fungal infections
• Bacterial folliculitis
• Acne
• Acute generalised exanthematous pustulosis (AGEP)
• Toxic erythema of newborn
• Grover disease.

What is the treatment for miliaria?

Management of miliaria requires heat and humidity to be controlled to reduce sweating and the avoidance of irritation to the skin. Strategies to avoid sweating and reduce irritation follow.

• Work in an air-conditioned office for at least a few hours a day.
• Sleep in a ventilated, cool bedroom.
• Move away from a tropical climate.
• Avoid excessive clothing and tight clothing.
• Avoid excessive soap and irritants.
• Wear shirts and blouses made of breathable synthetic fabrics or cotton.
• Remove wet clothing.

Treatment of miliaria may include:

• Cool water compresses 
• Calamine lotion to relieve discomfort; because of its drying effect, an emollient may be required.
• Treatment of fever with antipyretic such as acetoaminophen/paracetamol
• Mild topical steroids 
• Antiseptics and anti-staphylococcal antibiotics for secondary infection.

What is the outcome for miliaria?

Most cases of miliaria resolve within a day or two after changing to a cooler environment without any treatment or complications.