Hi Elizabeth - would need a bit more information about the use or oregano oil for thrush: Do you know how the mother used oil of oregano? Topical or internal? How much did she dilute the oil, if used externally? Was it removed 100% before baby nursed? Every time? Oregano ( Origanum vulgare) contains up to 1% volatile oil composed of fairly variable ( 0-90%) amounts of thymol and carvacrol - phenols both noted to have antifungal action and also for irritating skin. Many other constituents are also present - all would be concentrated in the essential oil. Commission E did do a monograph on Oregano leaf, but could not approve it for therapeutic use, due to a lack of evidence of efficacy. Andrew Chevallier (Encyclopedia of Medicinal Plants 1996) states that it is not to be used as a medicine in pregnancy, may be irritating to the skin ( I found this true especially if not diluted - it starts burning right away) and, as an essential oil, should not be taken internally. This doesn't sound like an ideal substance to treat thrush with!!! I would think that any remnant not removed from the breast would be taken into the baby's mouth. If very dilute, this may or may not cause irritation of their mucous membranes - but could. It would certainly be swallowed by the baby. Thus a lot would be riding on whether the mother properly dilutes the oil before use, and scrupulously removing what she can before nursing. One source I have here suggests if a person has asthma, excema or other skin sensitivities, great caution is required with any essential oil. Patch testing should be done first - reactions would be seen in 10-20 minutes but could go on for 24 hours. A reaction would require removal with generous amounts of vegetable oil in 2-3 repeat applications. Sorry -have only a general guideline for essential oil dilution: 5-10 drops into 20 ml (1Tbsp) carrier oil. I would want to know the specific amount for oregano before I used it on any body part, let alone thrush-infected nipples! Does anyone have a good suggestion for an oil-based product or something else to remove greasy medications or other nipple treatments before nursing??? Have heard mineral oil suggested, but this one doesn't set well with me. Ideally something non-allergenic, but not petrochemical. Sheila Humphrey BSc RN IBCLC [log in to unmask]