Earlier studies had raised concerns that acetaminophen (Tylenol) given during infancy might be connected to eczema, asthma, or other health conditions later in childhood.

"Our study found that paracetamol and ibuprofen are incredibly safe to use in young children," says lead researcher Professor Stuart Dalziel, Cure Kids Chair of Child Health Research at Waipapa Taumata Rau, University of Auckland, and Pediatrician at Starship Children's Hospital.

Dalziel notes that acetaminophen and ibuprofen are among the medicines most often prescribed or purchased over the counter for babies around the world.

"These results give parents and health professionals high confidence to continue to use these important medications."

Nearly 4,000 Babies Took Part

The trial followed almost 4,000 babies from birth across New Zealand. Half were randomly assigned to receive acetaminophen when medication was needed for fever or pain during the first year of life. The other half were assigned to receive ibuprofen.

At regular points throughout the study, parents were asked whether their children had experienced eczema, asthma symptoms, or bronchiolitis. The research team also reviewed prescription information and hospital records.

The findings from the first year of follow-up have now been analyzed and published in The Lancet Child & Adolescent Health.

No Significant Difference in Eczema or Bronchiolitis

About 16 percent of babies in the acetaminophen group developed eczema, compared with 15 percent in the ibuprofen group. Bronchiolitis affected about five percent of children in each group.

Researchers found that these differences were not statistically significant. Serious side effects were uncommon, and none were attributed to either medication.

Overall, the results showed no association between acetaminophen or ibuprofen and eczema or bronchiolitis. The findings also confirmed that both medicines were safe to use during infancy.

This is the first randomized controlled trial considered the gold standard for research to directly examine this question.

A Long-Term Study of Childhood Health

The findings are part of a larger research project called the 'Paracetamol and Ibuprofen in the Primary Prevention of Asthma in Tamariki (PIPPA Tamariki)' study.

PIPPA Tamariki is the largest clinical trial involving children ever carried out in New Zealand. Participants are being monitored from birth until they reach age six.

The research team plans to publish results from the children at age three, followed by additional findings when they reach age six.

The broader goal is to determine whether acetaminophen use during the first year of life is connected to health conditions that cannot be diagnosed reliably until children are older.

"We know that two-thirds of children who are wheezy at age three years don't develop asthma by age six," says Dalziel.

"Thus we need to wait until school age to ultimately test if paracetamol in the first year of life causes asthma."

Developmental conditions such as autism and attention deficit hyperactivity disorder (ADHD) also tend to be identified more accurately as children grow older.

Lead author Dr. Eunicia Tan, a senior lecturer at the University of Auckland and emergency physician at Middlemore Hospital, says, "Ultimately, the study will provide important evidence regarding the link between paracetamol use and asthma, eczema, hay fever, and developmental disorders, such as autism and ADHD."

The research was funded by the Health Research Council of New Zealand and Cure Kids. It was conducted by the University of Auckland and the Medical Research Institute of New Zealand, Wellington.