Maybe the simple causes are being overlooked.  What kind of diapers is mom putting on baby?  If she is using cloth, could the cause be detergent?  Has she tried rinsing in vinegar?

If disposable, maybe it is something in them. Has she tried switching brands to see if there is any difference? Has she tried letting the baby lie on a blanket without a diaper and get some air and sun on his sore little bottom?

Also, you mentioned that there are no signs of yeast.  Yeast is tricky.  Has she tried topical Nystatin on the baby's bottom?  If it is yeast, there should be some visible relief using something that is made to fight yeast fighting. 

I am not a yeast expert, but as the mother of five children I have seen plenty of diaper rash and have always been able to get through it without weaning.  And I have had painful nipples due to thrush with no visible yeast/ thrush on my nipples or in the mouths of the two I was tandem nursing.  My doctor cultured my nipples and treated all three of us.   I have also had a baby with a yeasty diaper rash with no thrush visible in his mouth and no nipple pain for me.

Good luck!

Nancy Sherwood IBCLC
Reston, Virginia

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