What are the causes of eczema?

Doctors do not know the exact cause of eczema, but an abnormal function of the immune system is believed to be a factor. Some forms of eczema can be triggered by substances that come in contact with the skin, such as soaps, cosmetics, clothing, detergents, jewelry, or sweat. Environmental allergens (substances that cause allergic reactions) may also cause outbreaks of eczema. Changes in temperature or humidity, or even psychological stress, for some people lead to outbreaks of eczema.