The prevalence of atopic eczema and other allergic disease has risen sharply in developed countries in recent decades, according to the research team.
Environmental and dietary factors are thought to play a part, they added.
To reach the conclusion, the research team quizzed the parents of 6 month old babies born in western Sweden in 2003 about their child's diet and any evidence of allergic eczema. They were quizzed again when the children reached the age of 12 months.
The children were all part of an ongoing health study, Infants of Western Sweden, which is tracking the long term health of almost 17000 babies.
Complete birth data and two sets of questionnaires were obtained for almost 5000 of the 8000 families contacted.
At six months, 13percent of families said that their youngest child had already developed eczema. By the time the children had reached 12 months of age, one in five had the condition.
The average age at which first symptoms appeared was 4 months.enes had a significant impact. Children with a sibling or mother who had the condition were almost twice as likely to be affected by the age of 12 months.
But breast feeding, the age at which dairy products were introduced into the diet, and keeping a furry pet in the house had no impact on risk. Around one in five households had a pet.
However, the introduction of fish into the diet before the age of 9 months cut the risk of developing the disease by 25percent. And a pet bird was also associated with a significant reduction in risk.