Antibiotics in pregnancy: what's the link to baby's eczema?

Atopic dermatitis, the most common form of eczema, affects about one child in five. Skin turns red, dry and itchy because a weakened barrier lets water escape and irritants in. It usually appears before the age of two and often fades by itself, but it can be the first step toward other allergies, such as food allergy, asthma and hay fever. Strictly speaking, "eczema" is the wider term, though most people use the two interchangeably. In children, this can be an early stage of what doctors call the "atopic march".

A small link, found again and again

Nearly one pregnancy in four involves antibiotics, according to an earlier review of about 34 million pregnancies. Researchers¹ from Hungary and Indonesia combined 30 studies on prenatal antibiotics exposure and more than 4.1 million mothers and 4.3 million children. After adjusting for factors such as the mother's age, allergies and smoking, children exposed before birth had 22% to 32% higher odds of eczema, depending on how the data were corrected for publication bias. This association concerns the odds of eczema, not a precise prediction of an individual child's risk. The link grew slightly with each additional course of antibiotics, and even a single course was associated with a small increase.

In three studies, the association grew with repeated antibiotic exposure, although the authors caution that the evidence is limited. This is an association, not proof of cause, and the authors rate the evidence as low certainty. The studies also lacked comparable data to distinguish exposure in the first trimester, second trimester or third trimester, so no firm conclusion can be drawn about the timing of prenatal treatment. It was clearest in European studies, and not seen in the US ones. The association was also not statistically significant in analyses restricted to larger studies or to eczema diagnosed from medical records. For one child the increase is small, the authors say, but with so many pregnancies and so many children affected, it may still matter across a population.

Why would a medicine reach the skin?

The leading hypothesis involves the microbiota. Antibiotics can disturb the microbes of a mother's gut and vagina, and a baby inherits its first microbes from her at birth. This early microbial exposure may help shape the child's developing immunity, making maternal microbiota a possible link between pregnancy and later skin health. Think of them as the first teachers of a young immune system: if the early lessons change, so might what it learns. The studies did not measure this directly. Nor could the researchers separate the effects of different antibiotic types, doses or treatment durations. Antibiotics given during labour showed no significant link, though only four studies looked. That finding does not rule out a birth-related association: the evidence for antibiotics around delivery was rated very low certainty.

None of this is a reason to refuse a treatment your doctor prescribes, since antibiotics remain essential for maternal infections. The authors recommend using antibiotic treatment in pregnancy when clearly needed, with an appropriate duration and choice of medicine. Eczema also has other roots, such as family history and variants of the filaggrin gene, which help the skin build its protective layer.