Catster is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

What Is a Cat’s Third Eyelid & What if It’s Showing? Vet Approved Advice

Written by: Codee Chessher

Last Updated on April 3, 2024 by Catster Editorial Team

Cat with third eyelid

What Is a Cat’s Third Eyelid & What if It’s Showing? Vet Approved Advice


Dr. Chyrle Bonk Photo


Dr. Chyrle Bonk


The information is current and up-to-date in accordance with the latest veterinarian research.

Learn more »

Cats have a unique anatomy. For instance, did you know that cats have not one or two eyelids, but three? It’s true! A cat’s third eyelid is technically called the nictitating membrane, located in the inner corner creases of your cat’s eyes. This eyelid serves an important function: producing and spreading a uniform tear film on your cat’s eyes using the tear glands. It helps them shrug off getting some dirt in their eyes as well as keeping the eyes hydrated, which are both important on the prowl. Lastly, it helps prevent infection in the eye.

You probably know about the regular top and bottom eyelids we share with cats—they protect the delicate eyes from harsh UV rays, dirt, dust, infection, wind, water, and other environmental hazards. Eyelids also lubricate the eyes and wash away most irritating particles before they can scratch the cornea. But what about if your cat’s third eyelid is showing with no other symptoms? Is that serious, or does it happen normally? It could be either, to tell the truth. Let’s dig in to find out normal times for when your cat’s inner eyelid is showing, as well as when to be worried and consult your vet.

cat paw divider

Is It Bad for My Cat’s Third Eyelid to Show?

Cat Eyelids
Feel free to use this image but please credit

No, it’s not necessarily bad for your cat’s third eyelid to show by itself. It may appear to protrude a little when your cat is very relaxed or sleepy, and it can also make an appearance when cats undergo anesthesia. These are both perfectly normal and a result of muscle relaxation. The third eyelid may also show when your cat is dehydrated, so make it your first order of business to top up their water bowl and see a vet before trying to diagnose more insidious health problems.

Potential Causes of a Protruding Third Eyelid

It can also be a bad sign when the third eyelid becomes visible. More specifically, it can signify an ocular condition, or even another health condition that is unrelated to your cat’s eyes.

When the third eyelid protrudes or appears to prolapse outward, you should take your cat to the vet. It’s possible they have one of several health conditions.

<strong>Health Conditions That Cause the Third Eyelid to Protrude:</strong>
  • Cherry eye: This dramatic-looking condition causes the third eyelid’s lacrimal (tear) gland to slip out of place and protrude outward. This condition isn’t usually painful in cats but can herald later ocular issues if untreated.
  • Conjunctivitis: Also known as pink eye, this painful eye infection causes inflammation on and around the eye and oftentimes makes the third eyelid protrude.
  • Corneal ulceration: Ulceration occurs when the epithelium, or outer layer of the eye, begins losing cells due to a wound, injury, or foreign contaminant. This can progress into ocular perforation or holes in the eye if left untreated.
  • Fever: High fevers from infections can dehydrate your cat’s body and can cause the third eyelid to jut outward.
  • Nerve damage: Nerve damage in the neck or face can cause protrusion of the third eyelid. It typically affects only one eye and can also affect the size of the pupil and muscle movement on one side of the face.
  • Glaucoma: Caused by fluid building up in the eye, glaucoma can push the third eyelid out to become more prominent.
  • Upper respiratory infections: Commonly caused by certain viruses, respiratory infections can result in inflammation that presses the third eyelid outward.
  • Haws syndrome: Haws syndrome is when both third eyelids protrude. The cause is unknown, but it is often related to inflammatory issues in the digestive tract.

When to Worry About Your Cat’s Third Eyelid

While it’s normal to see the third eyelid when your cat is relaxed or sleepy, you shouldn’t be seeing it every day. When accompanied by a few telltale signs, you can more exactly pinpoint what the cause could be. If your cat’s third eyelid is showing and they exhibit any of the below signs, visit your vet immediately.

<strong>Alarming Signs to Watch Out For:</strong>
  • Discharge from the eyes
  • Persistent redness or inflammation
  • Squinting
  • Pawing at the face or eyes
  • Fatigue or lethargy
  • Changes in appetite



It’s normal to see your cat’s third eyelid when they’re relaxed and sleepy. However, if you see the third eyelid protruding along with eye inflammation, pawing at their face, or other concerning signs, your cat might have a more serious condition, like conjunctivitis. Take your cat to the vet as soon as you notice these problems occurring to prevent them from becoming more serious later.

Featured Image Credit: Antoniya Kadiyska, Shutterstock

Get Catster in your inbox!

Stay informed! Get tips and exclusive deals.
Catster Editors Choice Badge
Shopping Cart


© Pangolia Pte. Ltd. All rights reserved.