Why do cats vomit hairballs
Cats vomit hairballs because they ingest fur during grooming, which accumulates in the stomach until it exceeds the organ's capacity to pass it naturally.
Cats vomit hairballs because they ingest fur during grooming, which accumulates in the stomach until it exceeds the organ's capacity to pass it naturally. This happens when the mass becomes too large to move through the intestines and the body expels it as a trichobezoar.
The grooming mechanism creates the problem
Cats are especially prone to hairball formation because they groom themselves by licking their fur, thereby ingesting it. Their tongues are covered in tiny, backward-facing hooks called papillae that act like a comb, pulling loose hair from the coat. While this keeps the cat clean, the hair is swallowed and enters the stomach where it cannot be digested.
Unlike food, hair does not break down in the acidic environment of the stomach. Instead, it accumulates over time, forming a tight elongated cylinder of packed fur. Occasionally, bits of other elements such as swallowed food may be included in the mass, but the core is almost entirely hair.
Why the stomach cannot always pass it
The stomach of a cat is designed to move food through the digestive tract, but it has limited ability to move a large, compacted mass of hair. When the hairball becomes too big, it blocks the normal passage of gastric contents. The body then triggers a vomiting reflex to expel the obstruction, as the mass cannot pass through the intestines.
This is a mechanical issue rather than a disease in itself, but it can be mistaken for other conditions. Animals with hairballs are sometimes mistaken as having other conditions of the stomach such as lymphosarcoma, tuberculosis, and tumor of the spleen. A trichobezoar is a bezoar, a mass found trapped in the gastrointestinal system, formed from the ingestion of hair.
When it becomes a medical emergency
While occasional vomiting is common, persistent vomiting warrants clinical evaluation to rule out gastrointestinal disease. Trichobezoars are rare in cats but can become fatal if undetected. Surgical intervention is often required when the mass is too large to pass naturally or if it causes a complete blockage.
It is important to distinguish between a routine hairball and a serious blockage. A dog or cat that suddenly loses interest in food, shows signs of pain, or vomits repeatedly without relief needs immediate veterinary attention. In extreme cases, the mass can cause general impairment of the digestive system, similar to the hazards seen in humans where hair cannot be digested or passed.
How fiber helps the process
Many owners use cat grass to aid the passing of hairballs. Cat grass is the colloquial term for trays or pots of young cereal grasses, most commonly wheat, barley, oat, and sometimes rye, that are grown indoors for cats to chew. Cats are believed to consume grasses primarily for their fiber content, which can help move the hair through the digestive tract.
A 2025 microscopy study of regurgitated matter found leaf trichomes interlocked with hair, suggesting that the rough texture of the grass helps bind the hair together and facilitates its expulsion. However, pet cat owners in surveys have not observed behavioral changes to support this hypothesis definitively. Regardless, cat grass is viewed positively in many cultures and can supplant nibbling on houseplants or lawn grasses.
Other species and the limits of vomiting
Not all animals can vomit hairballs. Rabbits are also prone to hairballs because they groom themselves in the same fashion as cats, but hairballs are especially dangerous for rabbits because they cannot regurgitate them. Due to the fragility of their digestive systems, hairballs in rabbits must be treated immediately or they may stop feeding and ultimately die from dehydration.
Cattle are also known to accumulate hairballs but, as they do not vomit, these are found usually after death and can be quite large. In humans, hairballs are uncommon but can occur when hair strands collect in the stomach and are unable to be ejected due to not enough friction with the surface of the gastric mucosa. This can result from trichophagia, trichotillomania, and pica, leading to a condition known as Rapunzel syndrome where the hairball can grow to significant sizes requiring surgical removal.
For most cats, occasional vomiting of a hairball is a normal physiological response to grooming. However, if the frequency increases or the cat shows signs of distress, it is a signal to consult a veterinarian rather than assuming it is just a hairball.