When cats are not sleeping or eating, they are grooming! All that hair goes down into the digestive tract, and in the stomach, can ball up into a hairball. Usually they are long and tubular when you find them on the floor since they take that shape as they come back up the esophagus.
Some cats seem to form lots of hairballs, others bring them up rarely or never. Long haired, thick-coated cats, such as the Persian, are more likely to build them up due to the sheer volume of their hair they take in. If the cat hunts mice, the hair also can contribute to hairballs.
Usually the hairballs do not cause problems and passes through the digestive tract to be incorporated into the bowel movements. Sometimes if they get large, the cat may have trouble bringing them up or passing the hair down and stomach irritation can result. Very rarely, hairballs can become large and hard, and need surgical removal.
Daily grooming removes a lot of dead hair so that less is ingested by the cat during self-grooming. If the cat is sensitive to fleas or other external parasites, over grooming may occur and increase hair intake, so make sure these parasites are eliminated.
Keep the haircoat in good health by feeding high-quality food. Some manufacturers make a hairball preventive diet. Sometimes omega fatty acid supplements are used to increase haircoat quality and skin health. Hairball remedies, such as petrolatum-based pastes, can be given at home by mouth. These often have extra vitamins added. Avoid administering plain mineral oil — cats cannot taste it and can inhale it and get pneumonia. As well, avoid plain petroleum jelly or vegetable oil since it does not have extra vitamins added to make up for the tendency for the petroleum to interfere with fat-soluble vitamin absorption.
Though cats can safely pass hair through the digestive tract, if your cat is having any signs of ill health, including vomiting, lethargy, reduced appetite or hard, small or scant feces, contact your veterinarian. Vomiting hairballs once or twice a month is not cause for concern, but if more frequent, discuss this with your veterinarian.