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Heat rash

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What is prickly heat?

Prickly heat, also known as miliaria, is an itchy rash of small, raised red spots that causes a stinging or prickling sensation on the skin.

The rash can develop anywhere on the body, but it most commonly occurs on your face, neck, back, chest and thighs.

The rash is made up of tiny spots or bumps that are surrounded by an area of red skin. The spots sometimes look like tiny blisters. They can cause mild swelling, itching and a stinging or intense prickling sensation.

Read more about the symptoms of prickly heat.

What causes prickly heat?

Prickly heat usually develops when a person sweats more than usual, such as during hot or humid weather. However, it is also possible to get prickly heat in the winter.

The condition is caused when the body's sweat glands become blocked. Excessive sweating can result in sweat becoming trapped beneath your skin. The trapped sweat causes skin irritation and the characteristic heat rash.

Read more about the causes of prickly heat.

Treating prickly heat

Prickly heat does not require any specific treatment and the rash usually disappears after a few days.

Avoiding the heat by staying in the shade and wearing loose cotton clothing will help ease your symptoms.

Applying calamine lotion will soothe the affected area of skin. You can also use hydrocortisone cream if your skin is particularly sore and itchy.

Read more about treating prickly heat.

Who gets prickly heat?

Anyone can get prickly heat but people who are overweight or obese are more likely to be affected. This is because they tend to sweat more than people who are slimmer.

Babies and children are also more at risk of getting prickly heat because their sweat glands are not fully developed.

Symptoms of prickly heat

The main symptom of prickly heat is an itchy rash that is made up of small, raised red spots.

The rash usually appears a few days after exposure to hot temperatures. Occasionally, the symptoms of prickly heat do not appear for several weeks or months.

Prickly heat rash

The prickly heat rash is made up of tiny spots or bumps that are surrounded by a patch of red skin. The spots sometimes look like tiny blisters and may cause:

  • mild swelling
  • itching
  • a stinging or intense prickling sensation

The rash can affect any part of your body but it most commonly develops on your:

  • face
  • neck
  • back
  • chest
  • thighs

However, it can also sometimes occur on your:

  • tummy
  • groin
  • armpits
  • hands
  • feet

The symptoms of prickly heat are usually worse in areas that are covered by clothing. This is because clothing can make you sweat and sometimes causes friction (rubbing).

Prickly heat causes

Prickly heat occurs when the body's sweat glands become blocked. Excessive sweating can cause sweat to become trapped beneath your skin, leading to skin irritation and a red rash.

If you sweat excessively, it is easier for dead skin cells and bacteria to collect in your sweat glands.

If your sweat glands become blocked, sweat will be trapped underneath your skin in tiny swollen pockets. It will also seep into the nearby tissue and irritate your skin.

When the pockets burst and release sweat, it causes a stinging and prickling sensation (prickly heat).

Risk factors

You are more at risk of developing prickly heat if you're in a hot climate where you sweat more than usual.

The following also increase your risk:

  • illness and immobility – long periods of time spent in bed can make you sweat more, particularly if you have warm bedding
  • wearing too much clothing, particularly in the winter
  • sitting too close to a fire or heater

Treatment for prickly heat

Prickly heat is not a serious condition and rarely requires specific treatment. The rash usually disappears after a few days.

However, if you have prickly heat, there are several things you can do to ease your symptoms:

  • Avoid excessive heat and humidity – if you need to go outside, spend time in the shade or take a small fan with you. Further exposure to the heat will cause you to sweat more and may make your rash worse.
  • Wear loose cotton clothing – avoid wearing synthetic fibres, such as polyester and nylon, which trap heat more easily than natural fibres.
  • Keep your skin cool – a cool bath or shower will cool you down, soothe your skin and help prevent further sweating. Staying in an air-conditioned room for a few hours a day will also provide considerable relief.
  • Use calamine lotion – this is available at most pharmacies and will help soothe sore and irritated skin.
  • Try hydrocortisone cream – low-strength hydrocortisone cream is also available from pharmacies and is effective at treating very itchy and irritated areas of skin. However, avoid using it on your face and always follow the instructions.
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