Cats have three eyelids for extra protection
While humans have two eyelids, cats have a special third one hidden in the corner of their eyes to keep them clean and moist!
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Last updated: February 3, 2026 at 03:17 PMWhile humans have two eyelids, cats have a special third one hidden in the corner of their eyes to keep them clean and moist!
Have you ever noticed a tiny white or clear triangle in the corner of your cat's eye when they are sleepy? That isn't a mistake - it’s actually their third eyelid!
Humans only have an upper and a lower eyelid. But cats (and many other animals like dogs and birds) have a special one called the "nictitating membrane" or the "haw." It is a thin, pale layer tucked away in the inner corner of the eye. Most of the time, it stays hidden, but it can slide across the eye horizontally like a windshield wiper.
The third eyelid has two very important jobs. First, it acts like a built-in cleaning cloth, sweeping away dust and dirt that might get stuck in the eye. Second, it helps spread moisture across the eyeball to keep it from getting dry. Since cats are hunters who often move through tall grass or bushes, this extra eyelid protects their precious eyes from getting scratched.
Usually, if your cat is wide awake and healthy, you won't see the third eyelid at all. You might catch a glimpse of it when they are very relaxed, halfway asleep, or just waking up. However, if the third eyelid stays visible for a long time while the cat is awake, it can be a sign that the cat is feeling sick or has an eye injury.
Cats have a third eyelid hidden in the corner of their eyes. It helps keep their eyes moist and protects them from dust or scratches while they are hunting. It’s like a built-in pair of safety goggles that pops out whenever they need it!