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Prickly heat

Published by Bupa's health information team, July 2009.

This factsheet is for people who have prickly heat, or who would like information about it.

Prickly heat is an itchy, red rash on your skin caused by blocked sweat glands. It's a common condition, particularly in young babies and people visiting hot countries or environments.

• About prickly heat
• Symptoms of prickly heat
• Complications of prickly heat
• Causes of prickly heat
• Diagnosis of prickly heat
• Treatment for prickly heat
• Prevention of prickly heat
• Questions and answers
• Related topics
• Sources

About prickly heat

Prickly heat (also sometimes referred to as miliaria), is caused by the sweat glands in your skin becoming blocked as a result of sweating. The sweat can't escape through the glands as it normally does so leaks into the skin layers below. This causes tiny spots and bumps to appear on your skin. The condition is usually made worse by hot conditions which cause you to sweat. Prickly heat is not an allergy.

There are three types of prickly heat, each relating to the layer of skin in which the sweat gland blockage occurs.

• Miliaria crystallina. The blockage is in the top of the upper layer of skin (epidermis). This type of rash is common in babies under two weeks old, as well as adults who have a fever or have recently entered a tropical climate. This rash is usually short-lived and doesn't require any treatment.
• Miliaria rubra. This is when the blockage in your sweat gland is in a deeper part of your epidermis. It commonly affects babies who are one to three weeks old and adults in hot, humid environments.
• Miliaria profunda. This is caused by a blockage in the deep layer of skin, the dermis. You usually get this after repeated bouts of miliaria rubra and is rare outside tropical countries.

Prickly heat can occur anywhere on your body, but usually appears on your neck and trunk.

Symptoms of prickly heat

The main symptom of prickly heat is a rash on your skin. Depending on the type of rash you have, this may or may not be itchy.

With miliaria crystallina, the rash is usually made up of small, clear spots. It isn't normally itchy or red. This type of rash is common in babies, especially on their head, neck and the upper part of their trunk. In adults, it usually occurs on the trunk.

Miliaria rubra causes red spots on your skin and the skin around the rash is also usually red. It can be very itchy and you may have a prickling sensation on your skin. In babies and young children the rash normally occurs on the neck and in the groin and armpits. In adults, the rash often occurs on the neck and scalp, as well as the upper part of the chest and back.

With miliaria profunda, the spots are quite large with a flesh-coloured head. The rash isn't usually itchy and normally occurs on your trunk, but can also appear on your arms and legs.

You may notice that the area of your body affected by the rash doesn't sweat, or you may have increased sweating in other parts of your body. You may also feel tired and unable to tolerate heat.

Complications of prickly heat

Complications of prickly heat are uncommon. Occasionally, a bacterial infection (staphylococci) can develop. However, only a small number of these cases require any treatment, usually with antibiotics.

If you have miliaria rubra or profunda, there is a risk that the lack of sweating may lead to heat stroke. Heat stroke is a serious condition caused by excessive heat. Your body is unable to control its temperature resulting in a sharp rise and dehydration.

Causes of prickly heat

Prickly heat is a common condition in babies, affecting almost one in 10. It's thought to be caused by under-developed sweat glands. These glands burst easily when a baby sweats causing the duct to become blocked.

In adults, the most common cause of prickly heat is being in hot, humid or tropical environments you're not used to. Research has also suggested that too much ultraviolet (UV) from the sun can cause prickly heat. Other causes include activity that makes you sweat a lot, such as sport, or having a high fever.

Some medicines have reportedly caused prickly heat such as neostigmine and bethanechol, used to treat urinary symptoms, Clonidine, a high blood pressure medicine, and isotretinoin, a treatment for severe acne.

Diagnosis of prickly heat

No tests are needed to diagnose prickly heat. However, if you keep having bouts of prickly heat, it's important to see your GP to rule out any other conditions that could look similar or those that could be causing it.

Treatment of prickly heat

Usually prickly heat goes away on its own and doesn't need any treatment.

Prickly heat caused by blockages deep in the skin can be uncomfortable and may lead to heat stroke. In these situations, treatment may be necessary.

The aim of treatment is to stop you from sweating. You may be advised to stick to cooler, air-conditioned climates, limit the amount of activity you do and not wear tight clothing. If you have a fever, your GP will give you treatment to bring your temperature down.

If your rash is particularly itchy or uncomfortable, try using cooling creams such as those containing menthol or calamine. Miliaria profunda has shown some benefit from lanolin creams.

Antihistamines are generally not helpful in this condition.

Prevention of prickly heat

There are several steps you can take to prevent prickly heat, especially if you are prone to it.

• Don't go into hot, humid environments. If you have to, try to become acclimatised to the heat slowly and stick to cool, air-conditioned places as much as possible.
• Wear loose, lightweight clothing in hot climates.
• Try not to sweat too much by over exerting yourself in hot environments.
• Seek advice if preventative measures are not working.

Related topics

• Impetigo

Sources

• Miliaria. eMedicine. http://emedicine.medscape.com, accessed 10 March 2009
• Simon C, Everitt H, Kendrick T. Oxford handbook of general practice. 2nd ed. Oxford: Oxford University Press, 2007:268
• Collier J, Longmore M, Brinsden M. Oxford handbook of clinical specialities. 7th ed. Oxford: Oxford University Press, 2007:121
• Miliaria. GP Notebook. www.gpnotebook.co.uk, accessed 10 March 2009

This information was published by Bupa's health information team and is based on reputable sources of medical evidence. It has been peer reviewed by Bupa doctors. The content is intended for general information only and does not replace the need for personal advice from a qualified health professional.

Publication date: July 2009