The most important point Sarah made while seeking a reason is - keeping up the milk supply on the refused side.  Sometimes there can be a reason that adults can recognise, e.g. following a bout of mastitis, but I've seen babies suddenly refuse for no known reason, other than to themselves. They've made some sort of connection about something they've heard or tasted or felt during a feed from that breast. If the supply is maintained, babies will often go back to that side again after several days or a week, or whatever works for that baby.

Some thoughts include: reduction of milk flow on that side, leading to the beginnings of involution and a saltier taste, perhaps through doing more of the feeding on the other side and not realising. It does happen!  A different, saltier taste can be an early sign of mastitis and so, even if the mother successfully prevented the development of full-blown mastitis, her baby might have noticed a change in taste on that side and objected.

As regards taste, forget about strong-flavoured foods the mother may be eating. If she ate them during pregnancy her baby will have tasted them in the amniotic fluid and the tastes are already familiar when they appear in her milk. (Some interesting studies by Julie Mennella and colleagues on this. So enlightening.)

Another point is that the baby needs to have pleasant associations of the breast - and so no crying while there. If she starts to cry, she needs to be moved away from that breast. I note that she will sometimes accept that breast when sleepy. Having a different cheek against that breast can sometimes help, e.g. by sliding her along so that her backside and legs are off the side of the mother, on the sofa. (No, I'm not talking football hold, just something simpler.)

Virginia
in Brisbane, Queensland, Australia

Sarah Riesenberg wrote:

Baby is 5 wks old and has recently started to refuse moms left breast, she has tried different positions but as soon as mom even brings the baby close to her breast she starts to cry. Mom has no history of any medical complications. Suggested mom take baby to dr to rule out any strained neck or ear infection baby got clean bill of health. Mom said that baby will take breast when sleepy but even the it rarely done. This has been going one for 1 week now. Right now we are protecting that sides milk supply by getting mom to ppm.
Any thoughts 

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