I agree with Mary Kay.  Nipples don't callous!  There are several 
reasons beyond the possibilites she states that nipples get less tender 
after the first few days:
- infants use less positive pressure (compression) and negative pressure 
(suction) as milk supply increases, which reduces stress on nipples.
- the increased milk lubricates the nipple and reduces friction.
I don't know where you can find good research on nipple soreness.  What 
there is pretty much says "pain is common in hospitals" = "pain is normal".
Catherine Watson Genna, IBCLC  NYC

             ***********************************************

To temporarily stop your subscription: set lactnet nomail
To start it again: set lactnet mail (or digest)
To unsubscribe: unsubscribe lactnet
All commands go to [log in to unmask]

The LACTNET mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software together with L-Soft's LSMTP(R)
mailer for lightning fast mail delivery. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html