Green stools happen. So do brownish, orange, and reddish; on top of the yellow seedy stools you are told to watch for in breastfed babies. Stools can be striped; a little brown and a lot of yellow for instance. Stools come in all shapes and sizes. Stools that indicate a medical emergency are black tar-like stools (in infants), white (all ages) and those containing blood (all ages). Please note - if you give your baby iron supplements that can cause black stools.
And to that note many supplements, either taken by you or given directly to baby; may cause stool discoloration. Examples of these include: colic calm (baby), gripe water (baby), fenugreek (mama). To tell if these supplements are the cause, discontinue for at least 48 hours and re-evaluate stool output then. (fenugreek specifically can cause a foremilk/hindmilk imbalance where there was not one before, which can lead to green stools. In addition, mamas who have a soy or nut allergy or a baby with soy/nut allergies or sensitivities should NOT take fenugreek to increase milk supply).
The occasional green stool is NOT a concern. If you eat a lot of green foods it can cause baby's stool to be green.
If your baby receives ANY formula; at all, and the stool is green this to is NOT an indication that there is a problem. Formula will change the color and consistency of baby's stools. This is true no matter HOW little formula you give. Even an ounce a day may have an affect.
If mom is lactose intolerant, but still eats/drinks foods that contain lactose this can also affect baby's stools.
Introducing solids will change baby's stools. Color, texture and consistency. Again, green stools after starting solids; totally normal.
Green stools CAN be a red flag however IF they are more common not.
Green mucusy stools CAN also be caused by a stomach virus and teething. Teething creates a lot of extra saliva and when swallowed can lead to stomach aches and stools that looks worrisome.
If baby has green mucusy stools AND ALL of the above bullet points have been looked at (mom's diet, any formula, supplements, solid foods, stomach virus and teething) AND the green stools are CONSISTENT then mom should look at 1) whether or not she has oversupply (creating a foremilk/hindmilk imbalance) or 2) baby has an intolerance or allergy to a food mom is eating (such as dairy or soy - FYI fenugreek is part of the soy family). One of the easiest ways to tell the difference between 1 and 2 - is the texture of the green stool. A milk imbalance will cause stools to look more foamy; whereas a baby with a food intolerance or allergy will have additional symptoms such being fussy, sleeping little, and skin rashes.
If an oversupply is suspected please refer to the documents on this board and keep in mind fixing an oversupply is a balancing act and will require a good deal of trial and error and many people do not see results overnight.
If a food allergy or intolerance is suspected please visit our DQ board dedicated to dealing with these issues. This too has no overnight fix, and while it may seem like formula is the answer it is NOT as most formulas contain the allergens you are trying to have baby avoid. They may prove to be a short term fix, but often in the long term the are not. Even during the food investigation process, it is better to breastfeed baby (or look into donor breastmilk) than to feed a baby with food sensitivities, formula.
All in all - the occasional green stool is NOT a problem. And before being concerned about oversupply or allergies - slow down and review the list of possible causes for green stool.
