I give lectures on body modifications and breastfeeding...and I have various piercings to include the nipples (sorry if that is TMI).  

When a piercing is healing some people get the 'crusties' which is serous fliud.  This is normal during the first stage of the healing process.  It comes and goes as the healing takes place.  During the final stage of healing (maturation) a piercing (of any type) creates a channel or fistula.  When the jewelry is taken out, the channel may or may not close afterwards.  Sebum (oil, keratin, cellular material) is produced by the body and collects in healed piercing sites and finds its way out via the channel created by the piercing.  Sebum is a moisturizer and also inhibits microorganisms on the skin.  Sebum is white, cheese-like, solid, and has a distinctive 'rotten' odor that is indicative of the cellular debris that it contains.  Sebum means the piercing has gone through all 3 stages of healing and is 'mature'.  

Pus on the other hand is foul-smelling, yellowish/greenish, and thick.  And is NOT normal in a healed piercing.  It indicates an infection.  

Sebum is not harmful, and as Jack Newman says (I am paraphrasing here), "wear sunglasses" and don't worry about it.  If this mother had never bothered to express the material and was just breastfeeding, she would never know the substance was there.  I would advise her to stop expressing it as there is no need to do so.  The baby may or may not care for the taste of the sebum.  

As to why the one side 'healed' and does NOT secrete a substance as opposed to the side that does....I wonder if the side that is NOT secreting is actually healed?  Also, sometimes piercings, especially the nipples, always secrete.  And some women find that it is more likely around their periods due to hormonal influence.  

As others have said, if she is truly worried she could have it cultured.  But my money is on it being sebum and nothing to worry about.  

As a side note I would, if I were her IBCLC, keep an eye on her milk production as some women have experienced blocked milk ducts due to scarring.  

Robyn Roche-Paull
BSN, RN, IBCLC
Proud owner of various piercings and tattoos
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