Heat rash occurs in babies when the pores of the sweat glands become blocked. This happens most often when the weather is hot or humid. As your infant sweats, little red bumps, and possibly tiny blisters, form because the blocked glands cannot clear the sweat.
Heat rashes and babies; Prickly heat rash; Red miliaria
To avoid heat rash, keep your baby cool and dry during warm weather.
Some helpful suggestions:
During the hot season, dress your baby in lightweight, soft, cotton clothing. Cotton is very absorbent and keeps moisture away from the baby's skin.
If air conditioning is not available, a fan may help cool your infant. Place the fan far enough away that there is only a gentle breeze drifting over the infant.
Avoid the use of powders, creams, and ointments. Baby powders don't improve or prevent heat rash. Creams and ointments tend to keep the skin warmer and block the pores.
Goddard DS, Gilliam AE, Frieden IJ. Vesiculobullous and Erosive Diseases in the Newborn. In: Bolognia JL, Jorizzo JL, Schaffer JV, et al, eds. Dermatology. 3rd ed. Philadelphia, Pa: Mosby Elsevier; 2012:chap 34.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.