Laura Aldag's rquest brought out the "incipient librarian brain" in me (eg., I tend to recall all kinds of trivia, but do not always remember WHERE I read it). Anyway, there is LOTS of data in the literature re: the ability of unrefrigerated fresh human milk to continue to kill bacteria for many hours. As for cleanliness, the issue is that cow's milk and formula are KILLED in order to make them drinkable. Homogenization and pasteurization involves heat treatment (usually several times) and this destroys any ability of the previously raw milk to kill bacteria. Not so with fresh (raw) human milk, which is loaded with white cells that just love to gobble up bugs. (the microscopic kind: one aside, my Siberian Husky adores grasshoppers,crickets and other bugs. Last night, I barely saved a froggie (who squeaked in terror!) from going down her gullet!) One study done in an African country near the equator found that human milk was fine more than 8 hours after expression in a room temperature about 85F most of the time. Another has shown up to 24 hours. Clean containers should be encouraged, but I opt for gerater flexibility for human milk if it has NOT been refrigerated/frozen and warning NEVER to use the same times for artificial baby milk, which has been shown to grow bugs VERY rapidly (within minutes!). Def. of LC service: "We are all faced with a series of great opportunities brilliantly disguised as impossible situations." Kathleen G. Auerbach,PhD, IBCLC - [log in to unmask]