In miliaria rubra, blocked sweat glands cause small, red skin bumps. In miliaria rubra, the blocked sweat ducts often appear as hundreds of small pink or red bumps, all approximately the same size and shape.
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Heat Rash or Prickly Heat (Miliaria Rubra)  A parent's guide for infants and babies

Picture of Heat Rash or Prickly Heat (Miliaria Rubra): In miliaria rubra, blocked sweat glands cause small, red skin bumps. Divider line
In miliaria rubra, blocked sweat glands cause small, red skin bumps.
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Overview
Miliaria rubra, also known as heat rash or prickly heat, is a common skin condition caused by the blockage of the sweat gland. Although this rash can be caused by fever, heat rash is more commonly seen in infants who are dressed too warmly (in the winter).
Who's At Risk
Heat rash is common in over-bundled infants in the winter and those who have recently moved to a hot and humid climate.
Signs and Symptoms
There are 2 forms of heat rash: miliaria crystallina, which consists of tiny clear fluid-filled blisters that pop and leave behind some scale; and miliaria rubra, which has similar clear fluid-filled blisters, but they are surrounded by red areas or tiny red bumps.

In infants, lesions of miliaria crystallina tend to occur on the head, neck, and upper part of the trunk. Miliaria rubra tends to occur on the neck and in the groin and armpits.
Self-Care Guidelines
Prevention and treatment of heat rash consist of controlling heat and humidity. Acetaminophen or ibuprofen can help to reduce fever. Remove any occlusive clothing, limit activity, and seek air conditioning or any cooler environment. Cool compresses can also help with the discomfort. Most infants recover uneventfully within a matter of weeks. Young infants should not be given fluids other than breast-milk or formula unless instructed by the child's doctor.
When to Seek Medical Care
The most common complications of heat rash include secondary infection from scratching and heat exhaustion.

Call your child's doctor if he/she is scratching significantly. There are medications that can help relieve the itching and, thus, prevent infection. Infected areas may need antibiotics. Call your child's doctor if the area develops pus, redness, crusting, swelling, or tenderness.

In cases of heat exhaustion, the skin will appear hot and flushed without any sweat. Your child may complain of dizziness, nausea, weakness, headache, confusion, or difficulty breathing. This can progress to heat stroke, so medical care should be obtained right away. Symptoms of heat stroke include a very high temperature, of 105°F or greater, decreased or loss of consciousness, or seizure.

Heat intolerance is recognized by a lack of sweating of the affected skin, irritable behavior, and a change in alertness. Call for emergency medical help if your infant shows one or more of the following symptoms:
  • Your baby is sweaty and restless, then suddenly lethargic and sleepy. If your baby is awake, he or she may seem sort of "glazed" and limp or go from flushed to pale.
  • Your baby shows signs of dehydration: a dry mouth, no tears with crying, cracked lips, sunken eyes, or has less than 1 wet diaper every 6–8 hours.
  • A decreased desire or ability to feed.
  • Vomiting.
  • Seizure.
  • It feels like he or she has a fever.
If you notice some combination of these signs, do everything you can to cool your baby off and have him or her seen by a doctor right away.

  • Get your child into the shade or into an air-conditioned space.
  • Undress your child and apply cool compresses.
  • Do not give fluids.
Treatments Your Physician May Prescribe
If there are signs of bacterial skin infection related to the heat rash or otherwise, oral or topical antibiotics may be given.

Dehydration may be treated with intravenous fluids, especially if there is vomiting. Heat stroke is treated by trying to quickly reduce the core temperature to normal. Immersion, evaporative, or invasive cooling techniques may be used in addition to rapid administration of intravenous fluids.



References

Bolognia, Jean L., ed. Dermatology, pp. 510, 578-579. New York: Mosby, 2003.

Wolff, Klaus, ed. Fitzpatrick's Dermatology in General Medicine. 7th ed., p. 730. New York: McGraw-Hill, 2008.
Last Updated: 22 Dec 2008