A chalazion is a small lump on the eyelid filled with trapped oil, immune cells, and inflammatory tissue. It forms when one of the tiny oil-producing glands in your eyelid becomes blocked, and the backed-up secretions leak into the surrounding tissue and trigger an immune reaction. Unlike a stye, a chalazion is not an infection. What’s inside is your body’s inflammatory response to its own misplaced oils.
How a Chalazion Forms
Your eyelids contain roughly 25 to 40 meibomian glands, small structures embedded in the firm tissue (called the tarsal plate) that gives your eyelid its shape. These glands produce an oily substance called meibum that coats the surface of your tears and prevents them from evaporating too quickly. Normally, meibum flows out through tiny openings along the edge of your eyelid every time you blink.
A chalazion starts when one of these gland openings gets clogged. The oil thickens and backs up behind the blockage. Eventually, the trapped secretions or their chemical breakdown products leak out of the gland and seep into the surrounding eyelid tissue. Your immune system treats this leaked oil as a foreign irritant and mounts an inflammatory response to wall it off and clean it up. That response is what builds the firm, round lump you can feel under your skin.
What’s Actually Inside the Lump
If you were to look at chalazion tissue under a microscope, you’d see a characteristic pattern called a lipogranuloma. At the center are pockets of trapped lipid (oil) surrounded by layers of immune cells. The oil itself dissolves during lab preparation, leaving behind distinctive clear spaces in tissue samples, but in a living eyelid, those spaces are filled with the waxy, degraded remnants of meibomian gland secretions.
Surrounding those oil pockets are specialized immune cells called epithelioid histiocytes, a type of white blood cell that has transformed into a cleanup crew. These cells cluster together and sometimes fuse into multinucleated giant cells, oversized immune cells formed when several smaller ones merge to engulf material too large for any single cell to handle. Mixed in are other immune cells, including lymphocytes, that sustain the ongoing inflammatory reaction.
Over time, the outer edges of the chalazion develop a fibrous shell, sometimes called a pseudocapsule, as the body attempts to seal off the irritating material. This is why older chalazia often feel quite firm and well-defined compared to the softer, more tender bump you might notice in the first few days.
Why It’s Not an Infection
People often confuse a chalazion with a stye, but they’re fundamentally different on the inside. A stye (hordeolum) is an active bacterial infection, typically caused by staphylococcal bacteria. An external stye develops in a hair follicle at the base of an eyelash. An internal stye develops in a meibomian gland itself. Either way, the contents include bacteria, pus, and the debris of an acute infection.
A chalazion, by contrast, is sterile. The inflammation is caused not by bacteria but by your own immune system reacting to leaked oil. Bacterial enzymes may play a role in breaking down the trapped meibum into more irritating compounds, but the lump itself does not contain an active infection. This distinction matters because antibiotics don’t resolve a chalazion. The problem isn’t a germ to kill; it’s a ball of oil and inflammatory tissue that needs to either drain or be reabsorbed.
How the Contents Are Treated
Because the core issue is solidified oil surrounded by inflammation, the first-line treatment is heat. Warm compresses applied to the eyelid for about 5 minutes at a time help soften and liquefy the trapped meibum. Research from the American Academy of Ophthalmology found that it takes 2 to 3 minutes of sustained heat on the eyelid surface to begin liquefying the oil inside. Once softened, the material can drain through the gland’s natural opening, and the immune response gradually subsides. Many chalazia resolve this way over several weeks.
When warm compresses aren’t enough, a doctor can surgically remove the contents. The procedure, called incision and curettage, is done from the inside of the eyelid so there’s no visible scar. A small vertical cut is made through the inner eyelid tissue, and the lipogranulomatous material (the mix of degraded oil and inflammatory cells) is drained. A small spoon-shaped instrument called a curette is then used to scrape out any remaining contents along with the fibrous pseudocapsule. Without removing that shell, the chalazion is more likely to refill.
When a Lump Isn’t a Chalazion
A rare but serious eyelid cancer called sebaceous gland carcinoma can mimic a chalazion closely enough that diagnosis is delayed by one to three years on average. The key warning signs that distinguish it from a simple chalazion include a lump that keeps coming back in the same spot after treatment, loss of eyelashes in the area around the bump, and diffuse thickening of the eyelid rather than a single well-defined nodule. A typical chalazion tends to be well-circumscribed and occurs more often in younger adults. Any eyelid lump that recurs repeatedly or doesn’t respond to standard treatment should be biopsied to rule out something more concerning.