Though many experts feel that the immune system is at least partially responsible for eczema, the specific cause of eczema is unknown. The immune system of someone with eczema may be oversensitive and overreact to substances that it mistakes as a foreign invader. Therefore, eczema is often common among families who have allergies since the causes of eczema are similar to allergic reactions.

The heredity of eczema causes is the sensitivity of the immune system. People in families may be affected by a variety of different allergens. The bodies of family members may react to allergens in different ways. Some family members may have asthma, eczema, or other allergy symptoms. The thing that the family members have in common is the hypersensitivity of the immune system.

Outbreaks of eczema can be triggered by different causes of eczema. It is difficult to identify specific eczema causes since many different substances can act as allergens. Some family members may be allergic to soaps or personal hygiene products while others may develop symptoms of eczema as a reaction to the weather or stress. Other possible triggers are environmental allergens, clothing, handling food, friction, jewelry, detergents, sweating, or bacteria.

With such a large spectrum of possible causes, the cause of eczema flair ups is almost impossible to determine unless the individual is aware of a new exposure. For example, if someone with eczema uses a new laundry detergent and had no current flair up of eczema prior to using it, the detergent may be the cause. In those cases in which the person with eczema may have used something new, they may want to discontinue the use of the new product. After the eczema is successfully treated, the person may want to try the new product again. If it causes a similar reaction, there is a good chance that the new product is the cause of eczema. The person should then avoid its use.

Using hypoallergenic products helps reduce the frequency of eczema flair ups in some people. Eczema causes are so individual that what helps one person in the family may cause flair ups in another family member. It is not uncommon for a family with members who have eczema to have to use different detergents and hygiene products for each of the family members. One family member may be fine using soap for sensitive skin while it may cause outbreaks of eczema for another family member.