A study of 4,000 children over eight years has found that the 'hygiene theory', which says that who are exposed to common diseases and play with other youngsters are less likely to develop allergies, is probably wrong.
Some people have believed that wrapping children in cotton wool, extensive use of household detergents and obsessive cleanliness has led to an increase in allergies.
Lead author Dr Johan C de Jongste, of Erasmus University in the Netherlands said: "We found no evidence for a protective or harmful effect of day care on the development of asthma symptoms, allergic sensitisation or airway hyper-responsiveness at the age of eight years.
"Early day care was associated with more airway symptoms until the age of four and only in children without older siblings, with a transient decrease in symptoms between four and eight years."
The findings are published in the American Journal of Respiratory and Critical Care Medicine.
Parents completed detailed questionnaires during pregnancy, at three months and one year and then annually until the child reached the age of eight, with answers on their child's day care and symptoms.
Children who started day care before the age of two were twice as likely to have wheezing in the first year of life than those who did not go to day care.
By the age of five the trend was no longer statistically significant and by the age of eight there was no link found between day care and wheezing.
Those who started day care later showed a similar but non-significant trend and there was no difference between boys and girls in the study.
Children who went to day care early and had older brothers or sisters wheezed the most, the study found, Telegraph.co.uk. reports
The choice of the city of Helsinki is not incidental as the capital of Finland had hosted US-Soviet negotiations on the limitation of nuclear stockpiles in 1969