Cat vomiting
People normalize cat vomit because hairballs are real. The trouble is that kidney disease, hyperthyroidism, intestinal disease, and toxins look like "just a hairball" until the cat is thin. Frequency and weight are the two facts that cut through the habit.
Hairball or illness
A true hairball is a damp wad of hair, usually produced with a single retch, in a cat who grooms a lot and then eats dinner. Liquid vomit with no hair, vomit several times a month, or vomit plus weight loss is not a grooming story. Bring a photo. Note whether food comes up right after eating (sometimes regurgitation or eating too fast) or hours later.
Blood, or brown liquid that looks like coffee grounds, should be seen promptly. So should vomiting with straining to urinate, which can be pain from a blocked bladder rather than a stomach bug. Male cats who vomit and visit the box without producing urine need an emergency clinic.
Toxins that cannot wait
Lilies, including many florist lilies and daylilies, can cause kidney failure in cats after a small exposure to pollen or vase water. That is an emergency even if the cat looks fine in the first hour. Permethrin from dog flea spot-ons causes tremors and is also an emergency. Human pain relievers, lilies, and essential oils do not belong in a "watch until morning" plan.
String is another classic. A cat who vomits and has thread under the tongue, or who ate a tinsel strand, may have a linear foreign body. Do not pull a long string that disappears down the throat. Pulling can saw through intestine.
Chronic vomiting
Older cats who vomit weekly often need bloodwork and a thyroid check. Hyperthyroidism and chronic kidney disease are common, treatable to a point, and easy to miss if everyone calls it hairballs. Inflammatory bowel disease and intestinal lymphoma can look the same from the outside: intermittent vomit, a picky appetite, and a slowly disappearing waist. Diet trials and imaging are clinic decisions.
While you wait for a booked visit, pull extra treats, keep the usual food, and pick up hair ties and plants. Do not start a rotating buffet. The checker and the not-eating guide cover the overlap between nausea and a skipped bowl. More topics sit on the vet help hub.
Sources
Clinic decisions belong to the veterinarian who can examine the animal. This page is background reading.
Cat vomiting questions
How often is cat vomiting too often?
More than once a week, or any day with repeated episodes, deserves a veterinary visit rather than another hairball paste.
What if the vomit is clear or foamy?
Foam can be bile or stomach fluid. If it happens often, or with weight loss, it is a medical workup, not a snack schedule tweak alone.
Are houseplants a concern?
Yes. Lilies are an emergency for cats even in small amounts. If a lily may have been chewed, go to a clinic now.