Adding fish to a child's diet before the age of nine months could reduce risk of eczema.
The rate of the painful skin condition has risen in Western countries in recent years, and scientists believe diet may be partly to blame.
Swedish researchers tracked the health of children in 5,000 families, and said that early introduction of fish cut the risk by a quarter.
The children were all part of an ongoing health study looking at almost 17,000 infants born in 2003 in western Sweden.
Some of the families involved agreed to fill in questionnaires about diet and home environment when the child was six months and 12 months old.
Any evidence of eczema was also recorded, and the results were analysed. At six months old, 13% of the families said their child had already developed eczema, and this rose to 20% by their first birthday.
Genes appeared to have the most powerful effect - children with a sibling or mother with eczema were almost twice as likely to be affected by 12 months.
Breastfeeding, the age at which dairy products were introduced, and the presence of a furry pet in the home had no detectable influence on eczema.
However, the introduction of fish before nine months cut the risk by 25%.
The research was published in Archives of Disease in Childhood.
The researchers wrote: "The fact that fish is rich in omega-3 fatty acids could partly explain the effects found in this cohort."
However, they said they found no measureable difference between children who ate white fish, and those who ate other types of fish richer in omega-3, making it hard to say for certain.
Dr George Du Toit, a paediatric allergy specialist, said that fish had been linked to allergic reactions and eczema.
He said: "The connection between diet and eczema is complex. Eczema, particularly severe eczema, is commonly associated with the presence of food allergy.
"Parents of young children with eczema may therefore wish to consult with their doctor prior to the introduction of foods that commonly cause allergy, such as cows milk, peanut and even fish."
A spokesman for the National Eczema Society welcomed the study, agreeing that the genetic component of the condition was likely to be the most significant, and urging parents to avoiding harsh soaps and detergents on the skin from a young age in families predisposed to the condition.
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