Stye and chalazion

A stye and a chalazion are both small bumps on the eyelid, and they start in the same place: the sebaceous glands, the glands that make oil. The difference is what happens inside. A stye, medically called a hordeolum, is an infection: it comes on suddenly and it hurts. A chalazion, on the other hand, is sterile, meaning no germs are infecting it; it grows slowly and usually doesn't hurt.

Both begin the same way, with a blocked gland. Think of a tube of ointment with a clogged tip: whatever is inside can't get out. In a stye, that blocked gland gets infected, most often by a bacterium called Staphylococcus aureus, and fills with pus until it forms a pustule, a small pimple full of pus.

A chalazion takes a different path. The oil stays trapped and breaks down, and what's left of it seeps into the surrounding tissue, the way a clogged pipe can eventually leak through a wall. The body responds with granulomatous inflammation, meaning it builds a small knot of inflammation around that oil. That's where the chalazion's technical name, lipogranuloma, comes from: lipo for fat and granuloma for that knot. And the two are connected: a stye that goes untreated, or that keeps coming back, can end up turning into a chalazion.