HAVING eczema as a child nearly doubles the risk of becoming an asthmatic later in life, according to research that lends strength to the aggressive treatment of childhood skin conditions.

In the largest study of its kind, researchers tracked 8500 Tasmanians from childhood to get the first concise picture of how allergic conditions develop.

The findings, published in the Journal of Allergy and Clinical Immunology, support the theory that eczema is often the first step in an allergic chain that leads to other related conditions such as hay fever and asthma.

People who had childhood eczema were more likely to develop childhood asthma or new-onset asthma later in life, or to have asthma that persisted from childhood into middle age, said lead author John Burgess, a population health specialist at Melbourne University.

"The incidence of asthma in people from the ages of eight to 44 who had childhood eczema was nearly double that of people who had never had eczema."