Miliaria (Prickly Heat)

It typically appears in hot, humid conditions or where clothing keeps skin warm and covered. When ducts near the surface become plugged, sweat backs up and irritates the surrounding skin. The rash often shows on the trunk, neck, or areas of friction and tends to ease once the skin cools and dries. It is common and usually self-limited, though widespread or persistent cases can prompt a check. Infants and people in hot climates encounter it frequently because their skin stays warm and moist. Because trapped sweat is the driver, letting the skin cool and breathe is central to how it settles. The prickling sensation gives it the everyday name prickly heat. The depth of the blockage within the duct can affect how the rash looks. Its strong link to heat and covering explains why it flares in summer or under heavy clothing.

Tiny itchy bumps across the back after a hot, humid day in heavy clothing are a classic picture of miliaria. The rash tends to fade once the person cools off and the skin dries, which reflects that trapped sweat, not an infection, caused it. A baby bundled in too many layers on a warm day may develop the same fine rash on the neck and chest.

It stems from blockage of the sweat duct, is worsened by occlusion that traps heat and moisture, and shares the tendency toward damp skin with intertrigo.