A case of gastrointestinal allergy in an infant caused by folic acid supplement taken by mother

We have described a case of a 38-day-old female infant with bloody stool attributed to gastrointestinal allergy to an over-the-counter folic acid supplement taken by the mother. She showed persistent bloody stool on day 5 of birth, and although her general condition was stable, she had approximately 10 diarrheal stools per day. The stool hemoglobin test showed positive results, and her peripheral blood eosinophil count was high (16%). She received mixed nutrition and was primarily breast fed. Her symptoms persisted despite suspending formula feeds. The blood in the stool promptly disappeared after discontinuing the over-the-counter folic acid supplement that her mother had been taking before her pregnancy. The fecal hemoglobin level increased again after her mother reinitiated supplement intake, thereby confirming reproducibility. Based on the patient's clinical course and the results of the skin prick and lymphocyte stimulation tests using the supplement and its components, the bloody stool was attributed to gastrointestinal allergy to the supplement transferred into breast milk. We speculated that the yeast contained in the supplement was the cause. Clinicians should be mindful of gastrointestinal allergies in infants caused by supplement use in mothers. When mothers take folic acid supplements, it is better to choose supplements with the lowest additives.