DermaTechRx Research Center

Prickly Heat Rash

Prickly heat rash or miliaria rubra is the most common type of heat rash. In this form of heat rash, the sweat duct becomes red and inflamed, and may cause a ‘prickling’ or stinging sensation. This type of heat rash may also cause mild itching. There are three types of miliaria, which are classified according to where the sweat ducts are blocked.

§  Miliaria rubra. Occurring deeper in the outer layer of skin, miliaria rubra causes red bumps that are intensely itchy or prickly, giving rise to its common name, prickly heat rash. There is often little or no sweating in the affected areas. Adults can develop miliaria rubra shortly after they’re exposed to hot weather, but the rash more often appears after several months of exposure. Infants usually develop this type of heat rash between the first and third weeks of life.

§  Miliaria crystallina. The mildest form of heat rash, this affects the sweat ducts in the stratum corneum, the topmost layer of skin. Miliaria crystallina is marked by tiny, clear, superficial blisters and bumps (papules) that break easily but aren’t itchy or painful. It usually clears on its own in a few days but can come back if hot, humid weather persists. And though it’s most common in newborns, adults can develop it, too, especially if they’ve recently moved from a temperate climate to the tropics.

§  Miliaria profunda. A less common form of heat rash, miliaria profunda occurs mainly in adults who have had repeat bouts of miliaria rubra. It affects the dermis, a deeper layer of skin, and appears soon after exercise or any activity that causes sweating. The lesions are firm and flesh-colored, much like goose bumps. Though it’s not uncomfortable, miliaria profunda can cause a widespread lack of perspiration, leading to symptoms of heat exhaustion, such as dizziness, nausea and a rapid pulse.

The best treatment for any form of heat rash is to reduce sweating by staying in air-conditioned buildings or, when that’s not possible, using fans to circulate the air, wearing lightweight clothing made of fabrics that breathe and limiting physical activity. Once skin is cool, heat rash tends to clear quickly.

Occasionally, heat rash becomes infected with bacteria, causing inflamed and itchy pustules. This is especially common in children in diapers but shouldn’t be confused with diaper rash, which results from irritation to tender skin, not from blocked pores.  In hot weather, people with miliaria profunda are at risk of heat exhaustion, which can cause low blood pressure, nausea, headache and a rapid pulse. Untreated heat exhaustion can lead to heatstroke, a life-threatening condition.