Does early-life antibiotic exposure meaningfully change infection risk?

How much does early antibiotic exposure actually raise infection risk?

The increase in risk is real but modest — typically in the range of 10–30% for serious infections. In a French study of nearly 3 million full-term infants, those exposed to antibiotics during pregnancy had a 12% higher odds of being hospitalized for an infection in their first year of life (adjusted odds ratio 1.12) [2]. A Swedish study of over 1.3 million infants found that prenatal antibiotic exposure was linked to a 28% higher rate of infections diagnosed in specialist care (adjusted hazard ratio 1.28) and a 15% higher rate of infection-related deaths in the first year [4]. For context, a 12–28% increase means that if the baseline risk of a serious infection is, say, 2%, it would rise to about 2.2–2.6% — a noticeable but not dramatic jump.

The effect is stronger when multiple risk factors combine. A Norwegian study of 45,485 children found that those whose mothers took antibiotics during pregnancy, who were born by C-section, and who were breastfed for less than 6 months had a 55% higher risk of hospitalization for infection by age 3, compared to children with none of those exposures [1]. This suggests that the impact on infection risk is cumulative, not just from antibiotics alone.

Does it matter when the antibiotic exposure happens — before birth, right after birth, or later in infancy?

Yes, timing matters, but the risk is present across multiple windows. Prenatal exposure (during pregnancy) consistently shows a small increased risk of infections in the baby's first year [2][4]. A large Swedish study that compared siblings to account for shared family factors found that the association weakened but did not disappear, suggesting that some of the risk is genuinely due to the antibiotics themselves, not just the mother's health [4].

Exposure in the first few days of life also carries risks, especially for very preterm infants. A meta-analysis of 11 studies found that early postnatal antibiotics in very preterm babies were linked to a 44% higher odds of bronchopulmonary dysplasia (a serious lung condition) and an 18% higher odds of necrotizing enterocolitis (a severe gut infection) [3]. However, for full-term infants, antibiotics given right after birth can actually reduce the risk of late-onset infection in the first week, as shown in a study of 88,574 very low birth weight infants — but this benefit came with a shift toward more resistant bacteria [6]. So the balance of benefit vs. harm depends heavily on the infant's health status.

Exposure during the first two years of life also appears to increase the risk of later infections. A Danish study of 614 children found that those with a high burden of common infections (like colds and ear infections) before age 3 had a 2.4-fold higher rate of moderate-to-severe infections later in childhood, and a 34% higher rate of antibiotic prescriptions, even after adjusting for social factors [5]. This suggests that early infections and antibiotic use may set up a cycle of vulnerability.

Is it really the antibiotics causing the risk, or is it the infections they were prescribed for?

This is the key question, and the evidence suggests it's a mix of both — but antibiotics do appear to have an independent effect. Several large studies have tried to separate the effect of the antibiotics from the underlying infection by adjusting for how often the child or mother had infections. For example, a pooled analysis of two Scandinavian birth cohorts (over 103,000 children) found that antibiotic use in the first year of life was linked to a 33% higher risk of inflammatory bowel disease (IBD), even after accounting for the number of infections the child had [8]. This points to a direct effect of the antibiotics, likely through disruption of the gut microbiome.

However, family genetics and shared environment also play a role. A Swedish study on atopic dermatitis (eczema) found that early-life antibiotics were associated with a 52% higher risk in the general population, but when they compared siblings (who share genetics and home environment), the risk dropped to 24% [7]. Similarly, a meta-analysis on autism and ADHD found that the apparent link to antibiotics disappeared entirely when sibling-matched studies were pooled [9]. This means that some of the observed risk is due to factors that run in families — such as a genetic tendency to get more infections — rather than the antibiotics themselves.

The bottom line: antibiotics likely contribute a small, real increase in infection risk, but the size of that effect is modest, and much of the association seen in simple comparisons is due to the fact that children who get more antibiotics are also the ones who get more infections for other reasons.

About These Sources

This answer is built on 9 peer-reviewed studies — published from 2021 to 2026, 5 from 2024 or later, 6 in Q1 journals, collectively cited 117 times — selected as the most relevant from 15 studies that passed quality screening, drawn from 44 papers retrieved from a database of over 500 million.

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