What is miliaria?
Miliaria (prickly heat) is a rash that develops in some people when
they sweat more than usual. The rash is sometimes called a 'sweat rash'
or a 'heat rash'. The rash is not usually serious, but it can be itchy
and uncomfortable.
What causes prickly heat?
Miliaria is due to blockage of sweat ducts. You have
thousands of sweat glands that lie just under the skin surface. These
glands make sweat which travels down the sweat duct to the skin
surface. If the sweat gland is blocked, the sweat seeps into the nearby
skin. This causes tiny pockets of inflammation which causes the rash.
What blocks the sweat ducts?
Some people are more prone to miliaria than others. It seems that a bacteria called Staphylococcus epidermidis may play a role. This bacterium lives harmlessly on the skin and miliaria is not
an infection. However, this bacterium makes a sticky substance. This
substance combined with excess sweat and dead skin cells may cause the
blockage. One study reports that people who develop miliaria when they
sweat have, on average, three times as many bacteria per unit area of
skin compared to those who do not develop miliaria when they sweat.
Anything
else that blocks the sweat ducts can also cause miliaria. For example,
if you place polythene tightly on your skin for 3-4 days, you are
likely to develop a miliaria rash on the covered skin.
Who gets miliaria?
Miliaria can develop in
anyone at any age. However, it is most common in children and babies as
their immature sweat glands are more prone to becoming blocked. It is
particularly common in newborn babies but soon clears.
Another
common time for the rash to occur is when people travel to a warmer
climate and sweat more than usual. Typically, on going to a hot country
for a holiday. Up to 3 in 10 people who travel to a warmer climate and
who sweat a lot may be affected by miliaria. The rash may begin within
a few days of arrival in the warmer country. However, it might develop
weeks, or even months, later.
Miliaria can also occur in cooler
climates when sweating is a problem. For example, people who lie on
their back for long periods due to illness (for example, after having a
stroke or a mjor operation) may get miliaria on their back.
What does miliaria look like and what are the symptoms?
There are three types of miliaria:
Miliaria crystallina
This is sometimes
called miliaria sudamina. This is caused when the blockage of the sweat
ducts is close to the surface of the skin. The rash is like tiny clear
spots that appear in crops. They may look like beads of sweat. The
spots tend to disappear within a few hours or days. This is the least
itchy form of the condition, and there may not be any itch at all. The
rash may simply be a curious event that you notice on your skin.
Miliaria rubra
This is the common type and
the one most people would identify as 'prickly heat'. This is caused
when the blockage of the sweat ducts occurs at a deeper part of the
epidermis (the outer layer of skin). Crops of tiny red bumpy spots
(tiny papules) develop. The spots are just a few millimeters in size
and may look like tiny blisters. Several crops of spots usually appear
in different parts of the body. They occur most where there is friction
with clothes. They can be very Itchy - although it may be more of an
intense prickling sensation. Some areas of skin become red.
The
rash may occur within days of coming into a hot climate. However, often
the rash does not appear until weeks or months have passed in the hot
climate. The rash tends to go within a few days if you get out of the
hot environment and stop sweating.
On the affected areas of skin
there is a reduced amount of sweat, or no sweat at all. You may feel
tired and become intolerant of heat. If you continue to sweat and the
rash covers a large part of your body, then you have a small risk of
developing a high fever and/or heat exhaustion. This is because you are
not able to sweat properly to get rid of body heat.
Miliaria profunda
This is uncommon. It is
caused when the blockage of the sweat ducts occurs at the level of the
dermis (middle layer of skin). This typically occurs in people who live
in a hot climate who have had repeated episodes of miliaria rubra.
Bigger lumps develop on the skin when you sweat. These tend to be
flesh-coloured as they are deeper than the miliaria rubra form. There
is little itch with this type of miliaria but there is a greater risk
of developing a fever and heat exhaustion if much of the skin surface
is affected.
For a list of websites that contain pictures of skin conditions including miliaria see www.patient.co.uk/showdoc/1097/
What is the treatment for miliaria?
In most cases the rash
will clear without any treatment. However, severe cases can last for
several weeks. One or more of the following may help to treat miliaria
and prevent further episodes from developing.
- If possible, avoid heat and humidity.
- Avoid further sweating. Even if this is possible for just a few
hours each day it can make a big difference. For example, staying in an
air conditioned room for a few hours a day. A cool bath or shower can
also be soothing and help to avoid sweating. Some people take frequent
cool showers to avoid developing the rash.
- Calamine lotion may cool and soothe the skin.
- Wear loose cotton clothing or clothing that has 'breathable' fabric.
- Using an antibacterial soap or antiseptic wash may help to keep the
number of bacteria on your skin down. This may reduce the risk of
developing miliaria.There are no research trials that have been done to
prove this, but it sounds sensible.
- Some people feel that moisturiser creams that contain anhydrous
lanolin help to to prevent blockage of the sweat ducts. If you are
prone to develop miliaria then it may be worth a try. Apply some to
your skin before activities that make you sweat or on arrival to a hot
climate.
- A steroid cream may soothe the irritation whilst waiting for the
condition to clear. Steroids work by reducing inflammation. You can buy
hydrocortisone cream, which is a mild steroid cream, from pharmacies.
It is best to use a cream rather than an ointment which may increase
blockage of sweat ducts.
If you feel generally unwell, you may be developing heat exhaustion. If this occurs, seek medical attention.
References
-
NA Levin Miliaria. eMedicine. Article dated January 25th 2007
-
Mowad CM, McGinley KJ, Foglia A, et al;
The role of extracellular polysaccharide substance produced by
Staphylococcus epidermidis in miliaria. J Am Acad Dermatol. 1995
Nov;33(5 Pt 1):729-33. [abstract]
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© EMIS and PiP 2008 Updated: 19 Mar 2008
