What causes eczema?

Atopic eczema

Atopic eczema is a genetically determined (hereditary) condition and results from over-sensitivity to external protein-based substances. This due to abnormal endogenous (internal) production of immune antibodies which precipitate an allergic reaction when the person comes into contact with substances (allergens) to which they have become sensitised. Allergens commonly involved are house dust mite, cat or dog fur or certain foodstuffs such as cow’s milk, eggs or nuts. Atopic eczema is commonly associated with other atopic disorders such as asthma and Hay fever.

Allergic eczema

This form of eczema occurs when the skin becomes sensitized to external substances. Initial contact with these substances causes no immediate problem but repeated exposure leads to sensitisation in susceptible individuals. Further contact with the sensitizer results in a reaction which causes an eruption of the typical eczematous rash. The rash may be localised to the site of contact but can be more generalised due to a systemic reaction.

Substances which can cause skin sensitization occur widely both in everyday life and in the working environment. The common ones are:

Irritant eczema

Often called primary irritant dermatitis this form of eczema is due to direct damage to the skin and does not require an allergic reaction to initiate the rash. Certain substances can cause skin damage and inflammation in most people, even those without an underlying tendency to become sensitized.

Substances which can cause irritant skin damage are:

• Acids
• Alkalis - caustic agents
• Detergents
• Fibreglass
• Abrasives and mineral dusts
• Mineral oils

Single episodes of contact may produce the eczematous rash or several episodes may be required before the irritant effect produces a reaction. Low grade repeated cumulative exposure may result in onset of eczema after several months or years as in domestic dermatitis.