Babies who took the over-the-counter pain reliever paracetamol in the first year of life were fifty percent more likely to show symptoms of asthma by the time they were six or seven years old, according to one of the studies.
Based on data collected on more than 200,000 children in 31 countries, the study also showed an increased risk of asthma symptoms in young children who had used the medication within the previous year -- the more frequently it was taken, the higher the risk.
Rates of eczema and rhinoconjunctivitis -- inflammation of the eye due to allergies -- also increased, according to the research, led by Richard Beasley of the Medical Research Institute in New Zealand and published in the British journal The Lancet.
Beasley and his colleagues stressed that their findings did not mean that parents should stop giving the drug.
"Paracetamol remains the preferred drug to relieve pain and fever in children," they said. "But it should be reserved for children with a high fever of 38.5 degrees Celsius (101.3 degrees Fahrenheit)."
A second study, also published in The Lancet, found that the first-time onset of asthma in adults aged 20-44 was closely linked to both rhinitis -- typically a runny nose caused by inflammation -- and allergies.
Using data from the European Community Health Survey, researchers at The National Institute of Health and Medical Research in France divided the subjects into four groups: those with rhinitis, with allergies, with both or neither.
The subjects were tracked over nearly a nine year period. Only one percent of the group that had neither ailment developed asthma, and almost twice as many of the allergy sufferers did.
More than three percent of adults with chronic runny noses wound up with asthma, and the rate jumped to nearly four percent for those who previously had both rhinitis and allergies.
A third study from the same special issue, led by Debra Stern of the University of Arizona in Tucson, showed a clear link between chronic asthma in early adulthood and several childhood conditions.
Follow up data on 850 infants covering a 20 year period showed, for example, that children who wheezed at age six were seven times more likely to become asthmatic.
The risk became 14 times greater for those who wheezed as adolescents.
"These findings identify a population at risk of chronic obstructive airway disease in early adulthood," noted Susanne Lau, a researcher at Charite University Medicine in Berlin.
"Whether therapeutic approaches at early preschool age can affect progression of the disease has yet to be established."