It is possible that there is an anal fissure.  Occasionally, babies
respond to foreign proteins in the mother's milk.  Most likely cause
of the latter is cow's milk protein.  If there is no fissure, then the
mother can try off milk products for a week or so to see if that makes
a difference.

However, if the baby is otherwise well, gaining well, content, I don't
think I would worry about it either.

Jack Newman, MD, FRCPC