There is no single cause of eczema. It probably has a mixture of inherited and environmental causes that act together at different times.
You may be born with an increased likelihood of developing eczema, which you inherit from your parents. When you are exposed to environmental factors, such as dust or pollen, this causes eczema to appear.
There are also several triggers, which can make your symptoms worse.
Genetic factors
Research suggests that atopic eczema is largely an inherited condition. This means that the cause lies in the genes that you inherit from your parents.
If a child's parents have atopic eczema, it is highly likely that the child will also develop the condition. Studies have shown that 60% of children who have a parent with atopic eczema also have the condition. If both parents have atopic eczema, there is an 80% chance that a child will also have the condition.
It is not yet known exactly which genes are responsible for eczema, although a protein called filaggrin is involved. Filaggrin attaches to a tough substance called keratin in cells and, along with other structures, forms a barrier at the skin's surface. If there is a problem with your filaggrin, the skin barrier can no longer provide effective protection from the environment.
There may be a problem with your filaggrin if you have inherited a defect in the gene responsible for making filaggrin. In this case, you have a higher risk of developing atopic eczema. The filaggrin gene may account for up to one in five cases of eczema. Other genes responsible for skin inflammation may also be responsible.
Environmental factors
If your genes make you more likely to develop atopic eczema, the condition will develop after you are exposed to certain environmental factors, such as allergens.
Allergens are substances that can cause the body to react abnormally. This is known as an allergic reaction. Some of the most common allergens that can cause atopic eczema include:
- house dust mites
- pet fur
- pollen
Atopic eczema can sometimes be caused by food allergens, especially in the first year of life. Foods that typically cause allergic reactions include:
- cows' milk
- eggs
- nuts
- soya
- wheat
Some studies of children and young people with atopic eczema, which were not carried out in the UK, found that one-third to nearly two-thirds also had a food allergy. Having a food allergy increases the likelihood of your atopic eczema being severe.
See the Heath A-Z topic about Food allergies for more information.
Allergies do not appear to play a role in many people with eczema. Other non-allergic factors may be just as important in bringing out eczema in someone who is likely to get it. These factor could include:
- cold weather
- dampness
- harsh soaps
- washing too much
- rough clothing
Triggers
Triggers can make atopic eczema worse, although they may not cause the condition.
Hormonal changes in women
Hormones are powerful chemicals that are produced by the body and have a wide range of effects. Changes in the levels of certain hormones can affect the symptoms of atopic eczema in some women.
Many women's eczema is worse at certain times during their menstrual cycle. Some women have a flare-up of their eczema in the days before their period.
Pregnancy, which causes hormonal changes, can also affect atopic eczema:
- More than half of all pregnant women find their symptoms get worse.
- One-quarter of pregnant women find their symptoms improve.
Stress
While stress is known to be associated with atopic eczema, it is not fully understood how it affects the condition. Some people with eczema have worse symptoms when they are stressed. For other people, their symptoms cause them to feel stressed.
See the Health A-Z topic about Stress for more information and ways to manage stress.
Exercise
After vigorous exercise, sweating may make your eczema symptoms worse. Try to keep cool when you are exercising by drinking plenty of fluids and taking regular breaks.
Irritants
Irritants can make your symptoms worse. What irritates you may be different to what irritates someone else with the condition, but could include:
- soaps and detergents, such as shampoo, washing-up liquid or bubble bath
- some types of clothing, especially wool and nylon
- overheating
- very cold, dry weather
- dust
- unfamiliar pets
Other triggers
Other possible triggers include:
- substances that touch your skin - such as perfume-based products or latex (a type of naturally occurring rubber)
- some food products - such as fish, peanuts and kiwi fruit, which can make your symptoms worse, although this does not mean you are allergic to them
- environmental factors - such as tobacco smoke, living near a busy road or having water that contains lots of minerals (hard water)
- the changing seasons - most people with atopic eczema find that their symptoms improve during the summer and get worse in the winter
