What should you look for?

Heat rash is also called prickly heat or miliaria. Its appearance can include solid raised spots, small fluid filled blisters, or pustules, meaning spots containing pus. The torso is the main area affected. Not every case has the same kind of spot, so looking only for blisters would miss other forms.1

Excessive sweating can cause heat rash. Sweating more in hot weather or during exercise is normal; sweating itself is not a diagnosis. Sweat is a clear, salty liquid made by glands in the skin, and its main job is cooling the body. As sweat evaporates, it cools the skin and the tissues underneath. Hot, humid conditions can make sweating insufficient to keep the body cool.234

Could it be another rash?

RashAppearance and useful clues
Heat rashSuperficial bumps, blisters or pus filled spots, mainly on the torso, associated with blocked sweat glands.
Contact dermatitisAn itchy rash where an irritant or allergen touched the skin. It can look red, purple or darker than the surrounding skin, with swelling, blisters, scaling or oozing.
Hives triggered by heat, exercise or emotional stressNumerous itchy raised welts, typically 2 to 3 millimetres across, surrounded by redness. Individual welts last 15 to 30 minutes.
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A rash after a new soap, fragrance, cosmetic or detergent deserves a closer look at contact dermatitis. Irritant reactions can appear quickly, while allergic reactions can take hours or days. The trigger and timing help distinguish rashes; appearance alone is not enough to diagnose yours.5

What can you do now?

Cooling is the priority for heat rash, so the bathroom shelf does not need to become a project. Calamine lotion may soothe the skin. The following steps also help ease itching in general.1

  1. 1Limit your time in the heat.
  2. 2Cool the skin with a damp towel or a cool or lukewarm shower.
  3. 3Change into loose cotton clothing rather than tight clothing.
  4. 4Pat or tap itchy skin instead of scratching, and keep your nails short and smooth.
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For itchy skin, avoid perfumed soaps, deodorants and moisturisers. Loose clothing has a practical role here, leaving an elaborate outfit with very little to contribute. A pharmacist can help choose an itching treatment; tell them where the rash is and about any other symptoms.6

What does heat rash look like on kids?

Heat rash is more common in young children. The general appearance is superficial bumps, blisters or pustules, but a child's new rash should not be identified by appearance alone.12

What does heat rash look like on the neck?

A neck rash is not automatically heat rash. Contact dermatitis commonly affects the neck, so consider whether fragrance, skincare or another substance touched that area, especially if the skin is swollen, flaky, burning or oozing.5

When should you get medical help?

See a doctor if itching is severe, affects daily life, does not improve with self care, keeps returning or affects your whole body. Get a worrying new rash checked. During pregnancy, discuss itching with a doctor or midwife.6

Confusion, dizziness, nausea, dry skin or a rapid, strong pulse during heat exposure can signal heat stroke. Get medical help immediately rather than treating those symptoms as a skin problem.2

Where this answer comes from

  1. 1Heat and colddermnetnz.org
  2. 2Heat Illness: MedlinePlusmedlineplus.gov
  3. 3Sweat | Perspiration | Anhidrosismedlineplus.gov
  4. 4What Is Sweat & Why Do We Sweat?my.clevelandclinic.org
  5. 5Contact Dermatitis: Symptoms, Causes, Types & Treatmentsmy.clevelandclinic.org
  6. 6Itchy skinnhs.uk