A new study published in Maternal & Child Nutrition investigated if subclinical mastitis (SCM) – an asymptomatic inflammation of the breast; maternal intestinal nematode and protozoan infections; and indicators of fecal-oral contamination or poor breastfeeding practices increased the odds of stunting, underweight or low head circumference in breastfed infants. This study recruited 105 mother-infant dyads from rural indigenous communities in Guatemala. Participants were subdivided based on whether the mother had SCM (milk Na:K ratio > 0.6). Maternal and infant anthropometry were measured at the time of breast milk collection; maternal stool samples were examined for the presence of intestinal nematodes and protozoa. Additionally, questionnaires were used to characterize breastfeeding practices (exclusivity, frequency) and support, hygiene (latrine use, household faucet), and infant diarrhea. The findings revealed that SCM occurred in 14% of women and was associated with increased odds of infant stunting, underweight offspring, and low head circumference. Although maternal pathogenic protozoa and nematodes were uncommon (<4%), non-pathogenic protozoa were common like Entamoeba coli (39%). Meanwhile, Entamoeba coli increased the likelihood of low head circumference whereas higher breastfeeding frequency lowered its incidence. Hence, it was inferred that prevention of SCM may improve early infant growth. Public health measures that increase breastfeeding frequency and reduce fecal-oral contamination may be required to minimize low head circumference.