Every cat owner has heard it at three in the morning: the slow, rhythmic hack-hack-hack from the hallway, the sound of a cat hunched low to the floor with its neck stretched forward, finally producing a damp, cigar-shaped wad of matted fur. It is so culturally familiar that most owners assume hairballs are simply part of the cat package — unpleasant, but normal.

The reality, according to current feline-medicine literature, is more nuanced. The occasional hairball is genuinely no big deal. A cat producing them every week, or a cat that retches dramatically without ever bringing one up, is sending a different signal — and in rare cases, hairballs become a true surgical emergency. Here is what the science actually says about why cats develop trichobezoars, what works to prevent them, and when to stop ignoring them.

What a Hairball Actually Is

The technical term is trichobezoar, from the Greek tricho- (hair) and the Arabic bezoar (a stone-like mass found in an animal's stomach). It is a damp wad of undigested hair, bound together by bile and gastric fluid. Despite the name "hairball," they are almost never round. As the Cornell Feline Health Center notes, regurgitated trichobezoars are usually slender and cylindrical — shaped like a cigar or sausage rather than a globe — because they take their shape from the narrow esophagus they are passing back up through.

Most are about an inch long, though they can reach five inches in length and an inch in thickness. The hair itself is keratin, which mammalian digestive enzymes cannot break down. Under normal circumstances the swallowed hair simply passes through and ends up in the litter box. A hairball forms when, for some reason, that transit fails.

Why Cats Swallow So Much Hair

Cats are obsessive groomers. Behavioral studies cited in feline-medicine reviews estimate that cats spend roughly 25% of their waking hours grooming, with some individuals devoting up to a third of waking time to it. Their tongues are covered in backward-facing keratin spines called papillae, which act like a fine-toothed comb — extremely effective at lifting loose hair off the coat and into the mouth.

How much hair is that? A 2018 study in the Journal of Animal Physiology and Animal Nutrition found that a short-haired adult cat loses roughly 28 grams of hair per kilogram of body weight per year, and that about two-thirds of all hair swallowed during grooming is recovered in the feces — meaning it passes through normally. The remaining third is, in principle, the population that risks becoming a hairball if gastric motility or transit time is not quite right.

When Hairballs Are Normal — and When They Are Not

Veterinary opinion has shifted over the last decade. A widely cited review in the Journal of Feline Medicine and Surgery ("Hair balls in cats: A normal nuisance or a sign that something is wrong?") argued that the field has been too casual about treating regular hairballs as a cat-owner inconvenience. Hair is not supposed to accumulate in the stomach. When it does — repeatedly — it usually means one of three things is happening:

Cornell's The Danger of Hairballs guidance is explicit on the threshold: a hairball every week or two is unremarkable, but more frequent hairballs — or any cat that retches without producing one — warrants a veterinary workup. The same goes for any cat that has never previously had hairballs and suddenly starts.

The Warning Signs of a Hairball Obstruction

The rare but serious complication is gastrointestinal obstruction. If a trichobezoar grows large enough that it can no longer pass through one of the narrow sphincters — either from the stomach into the small intestine, or further down the gut — the consequences escalate quickly. Veterinary Partner (VIN) and the Cornell Feline Health Center both flag the following as red flags requiring same-day evaluation:

True obstructions are uncommon, but they are a surgical emergency. Diagnosis usually involves abdominal radiographs or ultrasound, sometimes followed by endoscopic retrieval or, when that is not possible, open surgery. Supportive care typically includes intravenous fluids and a laxative such as lactulose or a petrolatum-based product to help the mass move through.

What Actually Prevents Hairballs

The good news is that for the great majority of cats, prevention is mostly a matter of two unglamorous interventions: brushing and fiber.

Brushing. The most consistently recommended preventive measure, across every major veterinary source, is regular grooming by the owner. Every gram of hair caught in a brush is a gram that does not end up in the cat's stomach. For short-haired cats this means a few minutes of brushing several times a week; for long-haired breeds, daily brushing is closer to the right baseline. A bristle brush, a fine-toothed metal comb, or a soft slicker will all work — what matters is consistency. Cats that hate brushing can sometimes be won over with very short sessions paired with food rewards.

Fiber. The fiber story is one of the more interesting findings in feline nutritional research over the last decade. A 2015 study published in the Journal of Nutritional Science found that cats fed a diet containing 20% sugarcane fiber for 42 days produced essentially zero large trichobezoars, compared with consistent trichobezoar excretion in cats fed a low-fiber control diet. The proposed mechanism is mechanical: long, insoluble fibers increase peristaltic stimulation, sweeping ingested hair down the gastrointestinal tract before it can clump in the stomach. A follow-up study combining sugarcane fiber with keratinolytic (hair-degrading) enzymes showed further improvement in fecal hair excretion. This is the science behind the "hairball control" diets sold by every major pet-food manufacturer — they are essentially higher-fiber recipes, and for cats with recurrent hairballs, the evidence that they help is reasonably good.

Hydration. A well-hydrated gut moves contents along more efficiently. Encouraging water intake — pet fountains, multiple water stations, a partial switch to wet food — is a low-effort intervention with broad benefits beyond hairballs.

Lubricant laxatives. Over-the-counter petrolatum-based pastes (the malty-flavored tubes sold under brand names like Laxatone) coat ingested hair and ease its passage through the gut. Veterinary guidance is generally that they are safe for occasional use but should not become a daily habit without veterinary input, since chronic use can reduce absorption of fat-soluble vitamins.

Treat the underlying problem. If a cat is over-grooming because of fleas, allergic skin disease, or anxiety, no amount of fiber will fully solve the hairball problem. The grooming itself is the driver, and the grooming has a cause. A cat suddenly producing more hairballs is often a cat trying to tell you something else is wrong.

The Short Version

A hairball every couple of weeks in a cat that is otherwise eating, drinking, playing, and using the litter box normally is, statistically, fine. Brush more, consider a higher-fiber food, and move on. But a cat that produces hairballs frequently, retches without producing one, suddenly starts vomiting hair when it never did before, or shows any of the obstruction warning signs above deserves a veterinary visit — not a tube of laxative paste from the pet aisle. The cigar-shaped wad on the rug is sometimes just biology. Sometimes it is the cat asking, in the only way it can, for someone to look closer.