Mary Ann O'Hara did a histology study on this, reference below. You can get the full abstract from the journal.
I think that the callous-type blebs are due to chronic friction. The worst (giant) I have ever seen occurred around 8-9 months in babies with untreated tongue-ties. It seems that when they started cutting teeth, they changed what they were doing enough to cause the start of a bleb. When mom stopped nursing on the one side temporarily, a bleb bloomed and grew equally on the other side. I have some pics of these monsters.
Hope this helps!
~Lisa Marasco
O’Hara, M. (2012). Bleb histology reveals inflammatory infiltrate that regresses with topical steroids; a case series [platform abstract]. Breastfeed Med, 7(Suppl 1), 2.
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