What Causes Eczema?

It must be very frustrating to ask your doctor why you have eczema only to get a vague answer suggesting several possible causes. The truth is that we don’t yet have a simple answer to this simple question – and we may never have. In this article, we will try to explain what our current understanding is and, just as importantly, try to dispel some of the myths that abound.

It may be easier to establish what does not cause eczema, but we fully understand that myths and untruths will arise if we do not fully understand the causes of eczema. It is important to do clear up misconceptions of the cause as they can lead to wholly inappropriate treatment and poorly controlled disease. If there were a simple answer to ‘What causes eczema?’, you would not be reading this!

As with much of this, we have many more answers related to studies on atopic eczema and contact eczema than on some of the other types, but the general messages are appropriate for all the different types.

Are there any common things that make eczema worse?

This depends to some extent on what type of eczema you are talking about. Much more research has been carried out in people with atopic eczema, so most of the answers to the more general questions relate more to atopic eczema than to the other forms.

It is safe to say that if you have large areas of contact eczema, your skin is likely to be irritated by the same sorts of thing that have come up in studies of atopic individuals.

Apart from the use of soaps and other things that can directly irritate the skin, the most common reasons are sweating (usually from exercise), fabrics (especially if the contact was at work) and hot weather. Fabrics encountered at work seem to relate not just to a direct irritant effect, but also to a physical friction effect if they have to be handled constantly as part of a job.

I want to find out exactly what is causing my son’s eczema. How can I get him tested?

You have asked one of the most difficult questions to answer because we do not have a complete understanding of the cause or causes of the various types of eczema. Your son is likely to have atopic eczema as this is the most common childhood form, so it is unlikely to be due to a single allergy, for which avoidance of the ‘allergen’ (the cause or trigger of the allergy) would result in a cure.

This approach might apply in contact allergic eczema, which is much more common in adult life, but even then there is usually more than one trigger. We do know that there is a strong inherited or genetic component to atopic eczema.

If you son has inherited a certain gene, or combination of genes, this predisposes him to being ‘atopic’, but he would still need some other trigger to cause him to have eczema.

To date, several genes have been identified that show a link with atopic disease, but it seems likely that there are other, as yet unidentified, genes that are important, and we hope that these will be discovered over the next few years.

We still do not understand the function of these genes as we do not know whether they can all lead to asthma, eczema or hay fever – the three atopic diseases – or whether individual genes are linked to just one of the diseases.

It is more likely that various different gene combinations can lead to atopic eczema as this would help to explain why different triggers are important in different patients and why eczema has more that one ‘cause’.

In other words, if your son has a susceptibility to developing eczema by having a particular group of genes, the eczema may be triggered by several different factors.

Despite much research, the evidence for any one trigger is very limited, and trials excluding or limiting exposure to different environmental factors (e.g. pets, woollen clothing, dust, car pollution) have been very disappointing in terms of improving eczema.

There is therefore no simple way to get your son tested, and it is more likely that simple detective work, looking at when it gets worse, may give you more of a clue.

But isn’t eczema caused by an allergy to something?

It depends what you mean by ‘allergy’. The strictly scientific definition of allergy refers to ‘when a substance causes an abnormally excessive response to arise from the body’s immune or defence system’. This may be measured by determining the levels of antibody in the white blood cells (lymphocytes).

The allergic reaction should be reproducible by ‘re-challenging’ with the same substance – the same reaction will be produced each time the substance is used. Many people, however, use the word ‘allergy’ in a different way.

They may use it to imply that a certain disorder is caused by a specific substance and that this disorder will disappear if the offending agent is avoided. Unfortunately, this is not the case with atopic eczema. It is perhaps best imagined as a built-in reaction that can be modified (but not caused) by the environment.

Many things in the environment can make eczema worse (e.g. woollen clothes, dog hair), but this may be because they act purely as an irritant rather than as a true allergen.

My GP says that my hand eczema is caused by things I come in contact with. What does this really mean?

Contact is the most common cause of hand eczema in adults. Your GP’s comment can be looked at in a couple of ways. First, some substances are potentially irritant to the skin such that anyone would eventually develop a rash that looked like eczema if they were exposed to high enough concentrations for long enough.

An example here is strong detergent. Your problem could be that you have a much lower threshold to a wide range of possible irritants, so you react to lower concentrations and a shorter contact time. This will especially be the case if you have a little bit of eczema or just dry skin at the time of the contact.

The same contact on an area of normal skin would not cause you a problem. The other possibility is that you are allergic to a particular substance (or several if you are unlucky).

This substance would be unlikely to cause any reaction in someone without an allergy to it no matter how long they were in contact with it, and it would be able to cause eczema on any part of your skin after the initial ‘sensitising’ reaction had taken place.

Your first contact that caused a problem would lead to eczema after a few days or so, but subsequent contacts would cause the eczema to start within a matter of hours. An example of this is an allergy to something in a perfume such as ‘balsam of Peru’.

What is the hygiene hypothesis?

In the late 1980s, it was noticed that large families seemed to have much less in the way of atopic disease. This was mainly found when studying asthma, for which the link is much more established than it is for atopic eczema. (The link does not apply to other types of eczema.)

It is thought that allergic diseases might be more likely to develop if the immune system of an infant or young child is understimulated from a lack of contact with infection, dirt, dust etc. The immune system is designed to allow us to develop protection against infections, so if a child is not exposed to any, the immune system finds something else to react to!

No single, specific infection has been linked to atopic eczema, so this is not an argument against immunisation, but it is worth avoiding unnecessary courses of antibiotics in early life and trying to be relaxed about children playing together and sharing germs and dirt.

Perhaps the old saying about ‘eating a peck of dirt’ has some validity. Some further support for the hypothesis has come from developing countries, where improvements in hygiene, and perhaps a better availability of treatment for worms and other gut parasites, seem to be linked to an increase in atopic disease.

What type of dog can I have that will not irritate my son’s eczema?

Dogs, and indeed any animals with furry or hairy coats (e.g. horses, cats), shed their hair and skin into the environment. These small particles are made up of proteins that are ‘foreign’ to humans. They can irritate the skin without an allergic reaction taking place, especially if the skin is already damaged with eczema.

They may also cause a genuine allergic response. Although breeds of dogs with shorter coats may spread their proteins around the house in lesser amounts, these will still be present in a significant quantity. All dogs therefore have the potential to make eczema worse, so it is probably best not to get a dog or other pet with a furry or hairy coat.

Are House Dust Mites Involved?

What are house dust mites? House dust mites are very small insects that are invisible to the naked eye. They are found in all of our homes, and they particularly like living in soft furnishings such as sofas, mattresses, carpets and duvets, where they are found in large numbers.

Modern standards of living, with central heating, seem to encourage their growth, and in practice they are difficult to eradicate completely. House dust mites do seem to be important in making asthma worse. Although their role in atopic eczema is less well established, they are worth taking seriously in some cases.

How do I know if my son is allergic to house dust mites? It is easy to find evidence of allergy to house dust mites by subjecting your son to skin-prick testing, but the result may not be very useful. Many people with eczema have a positive reaction to house dust mites – and to many other allergens that do not seem to make their eczema worse.

Many children without eczema also have positive reactions to house dust mites. If you suspect that house dust mites may be important in your son’s eczema, it may be best to try some avoidance measures rather than having the test done.

The test itself involves putting on to the skin drops of liquid that either contains mite extract in saline (salt water) or is just saline on its own. The skin is then pricked with a needle through each drop, and the skin’s reaction is tested. A strong reaction to mite extract compared with saline indicates a positive result.

I had a blood test at the hospital and have been told I am allergic to house dust mites. Is this a good test? This is probably a RAST test, which detects antibodies in your blood that react to different things. The test is good at detecting an allergy, but the link between having the allergy and actually getting problems on your skin is sometimes less clear.

It is certainly worth you trying all the avoidance measures. A RAST test is not able to detect general allergies as it is quite specific, so each test needs to focus on one possible cause or related groups of substances, for example dairy products, nuts or cats.

People keep telling me that the eczema on my hands is just a sign of stress. Is this true? Stress is mentioned as a cause or trigger of many different diseases, not just ones that affect the skin. It is easy to generalise but difficult to be sure in any individual case.

The best test may be to keep a diary of when your hands flare up and see whether this is related to times when you feel under stress. Some interesting work has been done looking at people’s reaction to stress as a risk factor for developing eczema on the hands.

It does seem that if you are someone who is more affected by stress and doesn’t deal with it well, you do have a greater chance of developing hand eczema. This is interesting as it relates to some of the ideas in homeopathy, acupuncture and other complementary medical philosophies that take account of the type of person you are when choosing a treatment.

To generalise a bit, the younger you are when you develop hand eczema and if patch tests are negative for allergy, the more likely you are to be affected by stress.