I agree with Barbara that these symptoms, pain, swelling, redness (and heat - is the reddened area warmer to touch than the surrounding breast?) do point to an inflammatory process the breast(s.) Pus can contain white blood cells, i.e. neutrophils, monocytes, microorganisms in various stages of digestion, and altered local tissue cells. Neutrophils secrete acidic subsances which could coagulate protein in milk. But once it were coagulated or curdled could it reverse? [If you add vinegar to milk it stays curdled.] It would seem hard to believe that these could be bacteria complexed with antibodies and agglutinated, but those could be consumed by the huge numbers of macrophages in early milk. Just speculating. Linda's mom with history of impetigo adds interest. Impetigo could be caused by either Strep or Staph but staph usually produces more pus (that is creamy yellow.) Even though there is no fever in Marie's mom, localized infection can occur with no systemic symptoms. All these other signs point to some infectious process. Culture of the milk and treatment might head off a possible abscess formation. If this started at day three could it be a hospital acquired wee-beastie? Mardrey