Miliaria is caused by blockage and/or inflammation of eccrine sweat glands.

Miliara crystallina is a type of miliaria formed of 1-2mm superficial blisters that easily break, without inflammation or erythema, usually seen on the head, neck and upper trunk in neonates. It is typically due to immature sweat ducts in a neonate, although can also be caused by fever, hot and humid environments or non-porous dressings in children and adults.

Often confused with milia, it is a distinct condition, but like milia, miliaria crystallina is a benign condition. It can rarely be complicated by secondary staphylococcal infection.

Miliaria crystallina is due to blockage of sweat ducts close to the surface of the skin, the epidermis. It is the most superficial form of miliara. A more common form, associated with hot climates, is miliaria rubra (slightly bigger at 2-4mm in size, red in colour, often with an erythematous background, due to obstruction of sweat glands in the deeper layers of the epidermis). Miliaria rubra is also benign.