Kids given antibiotics before their second birthday may have a heightened risk for chronic conditions like allergies and obesity, a new study suggests. The drugs’ effect on the microbiome might play a role in a baby’s future health, Mayo Clinic researchers said. The study analyzed data from more than 14,500 children. About 70% of these children were given antibiotics before age 2. Those kids were more likely to have multiple illnesses or conditions later in childhood, the study found. Early use of antibiotics increased the risk of asthma, allergic rhinitis, weight issues and obesity, food allergies, attention-deficit hyperactivity disorder, celiac disease, and atopic dermatitis. Types and frequency of illness depended on age, type of antibiotic, dose, and number of doses. There also were diff erences between boys and girls. Although antibiotics may only have a passing effect on the microbiome, they might also have long-term consequences, the clinic team theorized. However, the researchers noted the study cannot show a direct cause-and-effect relationship. “We want to emphasize that this study shows association, not causation of these conditions,” said Nathan LeBrasseur, a researcher at Mayo’s Kogod Center on Aging. “These findings offer the opportunity to target future research to determine more reliable and safer approaches to timing, dosing and types of antibiotics for children in this age group.” Although data show an increase in some of the childhood conditions found in the study, experts are not sure why. Other than the issue of drug-resistant bacteria, antibiotics have been presumed safe by most pediatricians, the researchers note.