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What Really Causes
Ovarian Cysts?
A plain-English breakdown of what’s actually happening inside your ovaries, month by month — and what happens when it doesn’t go to plan.
Your ovaries do this every single month, whether you notice or not: they grow a tiny fluid-filled sac, use it to release an egg, and then quietly dissolve it. Most of the time, it’s a flawless little process you’ll never feel. But sometimes that sac doesn’t pop the way it’s supposed to. Or it doesn’t dissolve on schedule. Or — in rarer cases — something else entirely starts growing where it shouldn’t. That’s an ovarian cyst.
Estimates vary by study and population, but somewhere between 1 in 10 and nearly 1 in 3 women will develop an ovarian cyst at some point in their lives. The vast majority are harmless and disappear on their own without you ever knowing they were there.
The Usual Suspect: Functional Cysts
Almost every ovarian cyst’s story starts the same place — ovulation. Each month, your ovary grows a follicle (think of it as a tiny, temporary water balloon) that matures and ruptures to release an egg. If that process doesn’t wrap up cleanly, you end up with one of two types of functional cyst.
Corpus Luteum Cysts
The balloon that forgot to deflate. After the follicle ruptures and releases its egg, the leftover shell — now called the corpus luteum — is supposed to shrink and disappear within a couple of weeks. When it doesn’t dissolve on schedule, fluid builds up inside it instead.
These can grow surprisingly large — up to roughly four inches across — and may even bleed internally. If the ovary twists around its own blood supply, or the cyst ruptures, you can feel a sudden, sharp pain that’s hard to ignore.
Follicular Cysts
When the egg never gets the memo. A follicular cyst forms when the mature follicle either never ruptures to release the egg, or simply collapses back in on itself. These tend to show up right around ovulation and can grow to over two inches.
When one ruptures, the pain shows up on one side of your abdomen, mid-cycle. That one-sided pattern is a useful clue — both this and corpus luteum cysts share the same basic origin, but tend to announce themselves a bit differently.
Dermoid Cysts
Here’s where things get genuinely strange. Dermoid cysts form from the same cells that produce your eggs — cells capable of developing into almost any tissue type in the body. The result? Cysts that can contain fat, hair, skin, teeth, or cartilage.
It sounds alarming, and it’s understandably unsettling to hear, but dermoid cysts are rarely cancerous. The real issue is size: as they grow, they can shift the ovary out of its normal position, causing it to twist and triggering severe abdominal pain.
Endometriomas
Endometriomas earn their nickname honestly — they’re filled with old, dark blood that gives them a brownish, syrupy appearance. They form when tissue similar to the uterine lining attaches itself to the ovaries, closely tied to endometriosis.
Unlike functional cysts, these aren’t a one-month timing glitch. They’re connected to a broader underlying condition, which is part of why they tend to need more attention from a doctor than a typical functional cyst would.
Pro Tip
Track where and when the pain happens. One-sided pain around the middle of your cycle points toward a functional cyst. Pain that’s more constant, worsens during your period, or comes with painful sex is more characteristic of an endometrioma. That detail alone can help your doctor narrow things down faster during an exam.
PCOS
Polycystic Ovarian Syndrome is its own category. Instead of one rogue cyst, PCOS involves numerous small cysts and a deeper communication breakdown between the hormones, brain, and ovaries — usually rooted in a failure to ovulate regularly. It disrupts the whole cycle rather than just one month’s worth of follicle development.
The causes behind ovarian cysts are about as varied as the cysts themselves — hormonal timing glitches, embryonic cell quirks, endometrial tissue gone rogue, or a full-blown hormonal feedback loop in the case of PCOS. Plenty of women carry one for weeks without feeling a single twinge.
When It’s Worth Getting Checked
- Sudden, sharp pelvic or abdominal pain
- Pain with fever, nausea, or vomiting
- Pain that doesn’t ease up over time
- Possible signs of rupture or ovarian torsion
If you’re experiencing any of the above, that’s worth getting checked rather than waiting it out — these can signal a rupture or ovarian torsion that needs prompt attention.