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Why Do I Get Heat Rash?

Heat rash shown on the underarm of a newborn
Heat rash is caused by clogged sweat ducts, which can happen due to perspiration becoming trapped under the skin.

Heat rash (also called sweat rash, prickly heat, or miliaria) is a type of heat-related illness that describes red bumps that form when sweat ducts become blocked.

The rash often appears on the head, neck, chest, or anywhere where the skin rubs together (such as the armpits, the creases of the elbows, and underneath the breasts).

You get heat rash because clogged sweat ducts cause perspiration to become trapped under the skin. Heat rash is more likely to occur in the following situations: 

  • Hot, humid weather or tropical climates (especially for people not used to these types of climates)
  • Being overdressed 
  • Intense physical activity that causes excessive sweating
  • Overheating
  • Underdeveloped sweat ducts

Babies and young children are more prone to heat rash because they are unable to regulate body temperature as well as adults.

What Are Symptoms of Heat Rashes?

Symptoms of heat rashes include:

  • Small, raised spots on the skin
  • May look like a cluster of tiny bubbles under the skin or like a cluster of small pimples
  • Skin redness (often less obvious on brown or black skin)
  • An itchy, prickly feeling
  • Skin irritation
  • Mild swelling

Heat rashes usually go away on their own within a few days. If heat rash does not go away within 3 to 4 days, see a doctor. Also see a doctor if you have a heat rash and symptoms of other heat-related illness including heat exhaustion or heat stroke (a medical emergency) such as: 

  • Core temperature elevated to usually more than 100° F (37.7° C) but not above 104° F (40° C) (heat exhaustion)
  • Body temperature of 104°F (40°C) or higher (heat stroke)
  • Pale, cool, moist skin
  • Profuse sweating
  • Dizziness or lightheadedness
  • Brain symptoms 
  • Fast heartbeat
  • Fast breathing (hyperventilation)
  • Dry skin
  • Skin redness (flushing) and warmth or heat
  • Vomiting or diarrhea
  • Headaches
  • Muscle cramps or weakness
  • Absence of sweating due to dehydration
  • Changes in blood pressure (may be high or low)

What Is the Treatment for Heat Rashes?

Initial treatment for heat rashes and mild heat-related illness usually includes:

  • Getting out of a hot, humid environment into a cool, dry environment 
  • Cooling measures such as cool baths or clean cloth dipped in cold water and applied to areas with rash or sunburn
  • Fluid intake
  • Rest/stopping physical activity
  • For skin itching: 
    • Calamine lotion
    • Antihistamines
    • Hydrocortisone cream 

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References
Image Source: iStock Images

https://www.uptodate.com/contents/miliaria?search=heat%20rash&source=search_result&selectedTitle=1~23&usage_type=default&display_rank=1

https://www.nhs.uk/conditions/heat-rash-prickly-heat/

https://www.uptodate.com/contents/heat-stroke-the-basics?search=Heat%20Stroke&source=search_result&selectedTitle=1~66&usage_type=default&display_rank=1