Background: Mothers who are unable to breastfeed their infants can obtain donor breast milk (DBM) from lactating mothers through milk banks (MB) or informal, “mother-to-mother” donation. Informal milk sharing is discouraged by the American Academy of Pediatrics (AAP), but has become increasingly popular, most likely through online milk sharing groups and personal anecdotes shared on parenting blogs. To date, however, no study has examined parental opinions and practices regarding DBM use expressed online. Purpose: To study parental practices and perceptions of receiving/donating breast milk (BM) via informal/formal routes, as discussed on publicly-accessible online blogs. Methods: Blog posts were identified by a Google search of “parenting blog AND donor breast milk” or “parenting blog AND milk sharing.” Posts about parents receiving/donating BM were categorized as formal/informal and donated/received; posts applicable to multiple categories were counted multiple times. Medical necessity for DBM, opinions regarding donation routes, concerns about DBM, presence of research evidence, and physician involvement were assessed. Results: Overall, 122 posts from 2010-present were analyzed (receiving, n=65; donating, n=57). Informal milk sharing accounted for 75.4% (n=49) of posts about receiving DBM and 69.7% (n=37) of posts about donating BM. Milk bank DBM recipients were more likely than informal recipients to have a medical necessity (75% vs 30.7%, p<.01), involve physicians (75% vs 26.5%, p< .01), and cite positive emotions (93.8% vs 61.2%, p< .05). Milk bank donors were more likely than informal donors to involve physicians (25% vs 2.7%, p<.05). Parents generally favored the donation route they utilized (p<.01). A thematic analysis of concerns with DBM found that disease transmission was a primary concern among users of both informal (recipients, 40.8%; donors, 21.6%) and formal (recipients, 31.3%; donors, 15%) routes. Bacterial contamination was also a main concern for MB recipients (31.3%). Conclusion: Given the prevalence of posts about informal milk donation, parents conducting online searches are more likely to find information about AAP-discouraged informal donation practices, most of which lacked important discussion of safety concerns. Furthermore, very few of those that partook in informal milk sharing discussed the practice with their physicians. It is therefore important that physicians proactively explain all milk donation options to parents and promote formal milk bank use while educating on the risks associated with obtaining BM informally.