Why do cats eat grass?

One idea is that cats use grass as an aid for feline indigestion. They lack the enzymes needed to digest grass, and so the individual blades either pass through their systems whole, or are regurgitated. Either way, the grass may help ease stomach discomfort and allow your cat to clear any indigestible matter (such as their own hair; or fur, feathers and bones from their prey) from their system.

It’s quite common for cats to be sick after eating grass – one study found that over a quarter of cats do this. Often, it’s not true vomit, but grass regurgitated with fur, feathers or other indigestible matter. A cat eating grass and vomiting isn’t normally a cause for concern, but if your cat is sick frequently (more than once a week) or you notice blood or mucus in their vomit, or they start foaming at the mouth, take them to the vet as soon as possible.

Scientists have discovered that the ancient ancestors of many meat-eating mammals, including cats and primates, would eat grass to help purge worms and other parasites from their digestive systems. The grass, being high in insoluble fibre, stimulates muscle activity along the digestive tract, helping them to expel the parasites in their poo.

This theory might explain why younger cats are more likely to eat grass, as they have immature immune systems and are more prone to parasites. So, a domestic cat eating grass may be showing instinctive behaviour that’s a throwback to their wild ancestors. But this doesn’t mean the habit is a substitute for worming. Even if your cat likes to snack on greenery, make sure they have regular, vet-approved worming treatments, too.

Yes – while chewing grass may be one of our cats’ more puzzling behaviours, it’s not usually a cause for concern. One study found that almost 90% of cats who have outdoor access eat grass.

If your cat likes to chomp on the edges of your lawn, don’t use chemical weed killers or pesticides that could be poisonous to them. If your cat has taken to nibbling your neighbours’ grass, ask them to avoid harmful chemicals, too, and consider providing a pot or tray of cat grass in your home.

If your cat likes to eat their greens, it’s especially important to make sure you don’t have any toxic plants or cut flowers around your home or garden. Lilies can be fatal to cats, and other common plants, such as daffodils, amaryllis and aloe vera, can cause vomiting and diarrhoea.

Usually it’s a harmless habit, but very rarely, a cat may get a grass seed or blade stuck in their nose or sinuses. If you notice your cat repeatedly sneezing, pawing their face, or with a runny nose or eyes after eating grass, take them to the vet to see if this could be the problem.

Your cat should also be checked out if you notice them eating much more grass than they normally do, if they vomit more than usual after eating grass, or if you suspect they may have eaten chemically treated grass. But, in general, don’t worry: eating grass is a normal habit in healthy cats.