Miliaria, often referred to as heat rash, sweat rash, or prickly heat, is a frequently encountered skin condition that results from blockage or inflammation of the eccrine sweat ducts. This obstruction can lead to an inability for sweat to properly exit the skin, causing irritation and characteristic skin lesions. Miliaria is particularly common in environments with high temperatures and humidity, making it prevalent in tropical climates, among hospitalized patients, and in newborns during the neonatal period.
The condition is classified into three distinct types based on the depth of sweat duct obstruction. Miliaria crystallina, also known as sudamina, occurs when the blockage is near the surface of the skin, specifically in the stratum corneum of the epidermis. Miliaria rubra, the most common variant, arises from deeper obstruction within the mid-epidermis and is known for its inflammatory symptoms. Miliaria profunda, sometimes referred to as tropical anhidrosis, is a deeper and rarer form in which sweat leaks into the dermis due to repeated episodes of miliaria rubra.
Miliaria can affect people of all ages and skin types. Miliaria crystallina often presents in neonates, typically within the first week of life, but can also occur in adults experiencing fever. Miliaria rubra is especially common in children and adults who are newly exposed to hot and humid conditions, such as those relocating to tropical climates. While this form of miliaria can emerge within days of exposure, it may take months to reach its peak. Miliaria profunda, although uncommon, is generally observed in adult males.
A number of factors can lead to the development of miliaria, most of which are related to increased sweating and occlusion of the skin. In infants, underdeveloped sweat ducts are a major contributing factor. Other common causes include intense physical activity, fever, and the use of non-breathable clothing or occlusive dressings. Hospitalized individuals, especially those confined to waterproof mattresses, are at higher risk. Miliaria has also been associated with drug-induced sweating, certain medications, radiotherapy, and rare genetic disorders such as Morvan syndrome and pseudohypoaldosteronism type I.
The symptoms of miliaria vary depending on its type. Miliaria crystallina manifests as small, clear blisters that resemble beads of sweat. These fragile vesicles are typically seen on the head, neck, and upper trunk, and they rupture easily, leaving behind a fine, bran-like scale. Miliaria rubra presents as intensely itchy red papules or papulovesicles, often accompanied by background redness. This form commonly affects the trunk and skin folds in children, while in adults it appears in areas subject to friction such as the scalp, neck, and upper torso. A variant known as miliaria pustulosa includes pustules, while miliaria profunda presents as asymptomatic, flesh-colored papules, usually on the trunk and limbs.
Complications of miliaria can include secondary bacterial infections, particularly from staphylococci, and impaired thermoregulation due to the skin’s compromised ability to sweat. In some cases, excessive sweating in unaffected areas may also occur.
Diagnosis of miliaria is typically clinical, based on the appearance and history of the rash. In recurrent or severe cases, a skin biopsy may be performed. Histological examination of miliaria crystallina shows vesicles associated with sweat ducts near the skin surface, while miliaria rubra is marked by spongiosis and vesicle formation. Tzanck smear testing can help differentiate miliaria from other blistering conditions like herpes simplex or toxic erythema of the newborn.
Several skin disorders can mimic miliaria, and it is important to distinguish it from conditions such as herpes simplex, fungal infections, bacterial folliculitis, acne, Grover disease, and other pustular eruptions like acute generalized exanthematous pustulosis (AGEP).
Treatment focuses on minimizing heat exposure, reducing sweat production, and preventing skin irritation. Effective management involves staying in cooler, well-ventilated environments, wearing breathable clothing, and avoiding heavy or tight garments. Skin care strategies may include gentle cleansing, the use of cool compresses or baths, and avoiding irritants such as harsh soaps. In some cases, topical agents such as calamine lotion can help soothe discomfort, although it may need to be paired with an emollient to prevent dryness. Antipyretics like paracetamol can be used to reduce fever, and topical corticosteroids may be prescribed for inflammation. If a secondary infection develops, antiseptics or anti-staphylococcal antibiotics may be necessary.
The prognosis for miliaria is generally excellent. Most cases resolve within a few days after moving to a cooler environment or adjusting personal care practices. With proper preventative measures and awareness, recurrence can be minimized, allowing individuals to maintain healthy, irritation-free skin even in challenging climates.
