What is ‘pus’ and is it present in milk?

Irish consumers can be confident that the milk they consume does not contain pus and is regulated to a high standard. The misleading myth that milk contains pus arises from a misconception that pus and white blood cells are the same thing. It is important to recognise that pus, a thick, light-yellow fluid, is a different substance, that is made up of dead white blood cells and tissue debris from inflammation, that accumulates locally at the site of an infection.

It is normal for healthy, uninfected cows, just like humans, to have a low level of white blood cells circulating in their bodies, and thus small numbers will always be present in the milk. These white blood cells have a surveillance role to play in alerting the immune system to the presence of bacteria.