Hydrocortisone (cortisol) is a normal component of breastmilk that passes from the mother's bloodstream into milk and might have a role in intestinal maturation, the intestinal microbiome, growth, body composition or neurodevelopment, but adequate studies are lacking.[1] Concentrations follow a diurnal rhythm, with the highest concentrations in the morning at about 7:00 am and the lowest concentrations in the late afternoon and evening.[2,3] Maternal stress can increase breastmilk cortisol levels.[4] Cortisol in milk may protect against later infant obesity, especially in girls;[5] however, in another study, milk glucocorticoid levels were positively associated with percent fat mass, adiposity and head circumference at 1 year of age.[6] Hydrocortisone has not been studied in breastmilk after exogenous administration in pharmacologic amounts. Although it is unlikely that dangerous amounts of hydrocortisone would reach the infant, a better studied alternate corticosteroid might be preferred. Maternal use of hydrocortisone as an enema would not be expected to cause any adverse effects in breastfed infants. Local maternal injections, such as for tendinitis, would not be expected to cause any adverse effects in breastfed infants, but might occasionally cause temporary loss of milk supply. See also Hydrocortisone, Topical. Hydrocortisone concentrations in breastmilk are not affected by storage for 36 hours at room temperature, during multiple freeze-thaw cycles, nor Holder pasteurization (62.5 degrees C for 30 minutes).[7-9]

Topical hydrocortisone has not been studied during breastfeeding. Since only extensive application of the most potent corticosteroids may cause systemic effects in the mother, it is unlikely that short-term application of topical hydrocortisone would pose a risk to the breastfed infant by passage into breastmilk. However, it would be prudent to use the least potent drug on the smallest area of skin possible. It is important to ensure that the infant's skin does not come into direct contact with the areas of skin that have been treated. Only water-miscible cream or gel products should be applied to the breast because ointments may expose the infant to high levels of mineral paraffins via licking.[1] Hydrocortisone can be applied to the breast or nipple area, but should be wiped off thoroughly prior to nursing.[2] Maternal use rectally with a cream or by suppository poses very little risk to the breastfed infant.