Breast buttons develop in a location similar to that of breast blisters (see Breast Blisters in Poultry Breast Blisters in Poultry Fluid-filled sternal bursa characteristic of breast blister on the keel of a turkey. In chickens and turkeys, a bursa lined with synovial membrane is normally present over the anterior projection... read more 
). They have a localized, hard crust on the surface and a core of dead skin and chronic inflammation extending into the subcutis. The cause is not well defined, but a breast button may start as a chemical burn due to prolonged contact of poorly feathered skin with wet litter containing ammonia or toxins. The presence of good quality, dry litter is associated with a reduced number of affected turkeys.
