If you’ve ever scratched/shaved/popped a zit, you know that sometimes it leaks white stuff, sometimes it leaks blood - and sometimes, it leaks clear fluid.
The white stuff, as I understand it, is a mix of skin cells, sebum, and pus (due to infection).
Depending on how aggressive you are about rupturing and squeezing the zit, you may also get blood.
So what the heck is the clear liquid that sometimes seems to leak out for minutes on end?
Serum.
Serum could mean two things.
One is serious fluid, which originates from various internal glands.
I assume you’re speaking instead of blood serum? If so, how does blood serum leak from a wound like this? Wouldn’t the whole blood clot and plug any leaking blood vessels?
Lymph The same stuff you see when you break a blister.
The fluid isn’t coming directly from the vessel, it’s extracellular. Your skin isn’t intact inside the zit pocket, so it leaks out. Kind of like a blister.
Kind of like SeldomSeen said 