Why does the skin on my cat’s back twitch or ripple?

In most cats this is just a reflex, the same twitch you would get from a fly landing on your arm, and it is especially common along the lower back where the skin is thin and sensitive. It happens more during petting sessions, especially if you are close to the base of the tail, and does not mean the touch is unwanted on its own. It becomes worth a closer look when the twitching is frequent even without being touched, comes with dilated pupils, sudden aggression or the cat seeming to react to and then attack her own skin or tail, a pattern sometimes called feline hyperesthesia.

When to call a vet: Frequent unprompted skin rippling, especially with sudden aggression or tail-chasing, is worth discussing with a vet.