Why?
Kittens make an enzyme called lactase to digest their mother's milk. After weaning, many cats make much less of it, so the lactose in milk isn't broken down and ferments in the gut instead. That leads to gas, bloating, diarrhea and sometimes vomiting. The classic saucer of milk is a cartoon image, not good advice.
How much?
It's best to skip it entirely. Whole, 2% and skim milk all contain lactose, and so does goat's milk. What your cat really needs is fresh water, always available.
The risks
- Diarrhea, sometimes within a few hours
- Bloating, gas and belly pain
- Vomiting
- Extra calories, especially with whole milk
Your cat ate some: what now?
A few laps of milk usually aren't serious; the worst case is a mild upset stomach. Keep an eye on the litter box for 24 to 48 hours and make sure fresh water is available. If the diarrhea lasts, your cat vomits repeatedly or seems lethargic, call your vet.
Better options
If you want to give a treat, look for lactose-free milk made for cats, sold in pet stores and supermarkets. A spoonful of the cooking water from plain chicken, with no salt or onion, is often just as popular.
Common questions
Can kittens drink cow's milk?
No. Cow's milk doesn't have the right makeup for kittens and can cause diarrhea, which quickly becomes dangerous at that age. An orphaned kitten needs a kitten milk replacer, ideally with guidance from a vet.
Is lactose-free milk OK for cats?
Lactose-free milk for people is easier on the stomach, since the problem sugar has been broken down. It's still fatty and adds nothing your cat needs, so a small amount of milk made for cats is a better choice.
This information is general and does not replace advice from a veterinarian. If your cat has swallowed something toxic, call your vet or an animal poison control center right away, without waiting for symptoms.