The use of acetaminophen in the first year of life is associated with an increased risk for asthma, eczema and allergic runny nose. Acetaminophen is sold in the United States under the brand name Tylenol, and is used as an ingredient in many other pain relievers.

The study looked at data from more than 190,000 children in 28 countries. Their parents responded to questionnaires about various health and diet practices. After controlling for numerous factors, the study showed that children given acetaminophen before age 1 had an almost 50 percent increased risk for asthma, eczema and allergy.

The study is large, but the conclusion is not certain; the medical information was obtained from parents after the fact, and children with asthma and related illnesses may be more likely to be treated with acetaminophen in the first place.