Is your cat’s third eyelid showing?
That pale flap is rarely harmless.
It often means illness, injury, or dehydration.
The third eyelid normally hides in the inner corner, so when it stays visible your cat is giving you a clue.
In this post we’ll explain what that clue can mean, what to watch for at home, and simple checks and urgent signs that need same-day veterinary care.
Understanding Why a Cat’s Third Eyelid Becomes Visible
Your cat’s third eyelid is called the nictitating membrane. It’s a thin layer of tissue tucked into the inner corner of each eye. Most of the time you won’t see much of it, just a pale sliver near the nose. This membrane sweeps across the eye to spread tears, clear away dust and pollen, and shield the cornea from scratches. When your cat blinks, the membrane slides back into place. When the eyeball pulls back slightly, the membrane rises to cover part of the eye. Unlike the upper and lower lids, your cat can’t control the third eyelid on purpose.
Seeing the third eyelid for a few seconds when your cat first wakes up is totally normal. As they stretch and open their eyes fully, that translucent layer should disappear. The same thing happens after anesthesia or sedation. Muscles relax, the eyeball sinks back a bit, and the membrane rises. This usually clears up within hours as your cat becomes alert again. If the third eyelid stays partially raised for more than a day, or if it appears suddenly in an otherwise healthy cat, the cause is almost always illness, injury, pain, or dehydration.
When the third eyelid stays elevated, something’s wrong. If one eye shows the membrane and the other looks normal, the problem is likely focused on that eye or the nerve supply to that side of the face. When both third eyelids are visible, think about systemic problems. Dehydration, fever, gastrointestinal upset, parasites, or conditions affecting the whole body. Cats in pain or discomfort often show the third eyelid as a reflex of eye retraction or muscle weakness. Even when your cat seems to act normally otherwise, a consistently visible third eyelid warrants a vet exam to prevent eye damage and catch underlying disease early.
Watch for these urgent care warning signs:
• Sudden onset in one or both eyes within hours, especially if your cat was fine the night before.
• Lethargy, collapse, or difficulty standing. Any sign your cat is weak or unsteady.
• Severe swelling or bulging of the eye, redness covering the entire white of the eye, or thick yellow or green discharge.
• Neurological symptoms like head tilt, uneven pupils, disorientation, or facial asymmetry.
• Refusal to eat or drink for more than 12 hours, paired with visible third eyelid.
• Evidence of trauma. Blood around the face, visible wounds, or history of a fall or fight.
Common Medical Causes Behind a Visible Third Eyelid
Eye infections rank among the most frequent causes of third eyelid elevation in cats. Conjunctivitis, commonly called pink eye, inflames the delicate tissues around the eye and causes swelling that pushes the third eyelid forward. Bacterial and viral infections both produce this effect. You may notice redness, squinting, and discharge that ranges from clear and watery to thick and yellow. Upper respiratory infections, especially those caused by feline herpesvirus, often trigger conjunctivitis in one or both eyes. The third eyelid rises because the eyeball itself may pull back slightly from pain, or because swollen tissue physically crowds the space around the membrane.
Haws syndrome is a condition that causes both third eyelids to rise at the same time, covering roughly a quarter to a third of each eye. The cause isn’t fully understood, but vets link it to gastrointestinal upset. Many cats with Haws have recently had vomiting or diarrhea, or they live in households where another pet has shown GI symptoms. Some cases appear with no obvious stomach trouble at all. The good news is that Haws syndrome usually resolves on its own over days to weeks. The third eyelids gradually slide back into place as the underlying GI inflammation settles. Recurrent episodes suggest chronic intestinal issues like food sensitivity or inflammatory bowel disease, and those cases benefit from dietary changes or further workup.
Systemic illness and dehydration also trigger third eyelid visibility. When a cat runs a fever or loses fluids through vomiting, diarrhea, or simply not drinking enough, the fat pad behind the eyeball shrinks. The eye sinks back slightly into the socket, and the third eyelid rises to fill the gap. Parasites like tapeworms can cause chronic weight loss, weakness, and poor body condition that shows up as sunken eyes and visible membranes. Any illness that saps your cat’s strength or hydration status can produce this sign. Kidney disease, diabetes, severe infections. If your cat feels warm to the touch, has dry gums, or shows loose skin that doesn’t spring back quickly when you gently lift it, dehydration is likely.
Injury and neurologic problems round out the common causes. A scratch to the cornea, a foreign object like a grass seed lodged under the eyelid, or blunt trauma from a fight can all cause pain that makes the eye retract. Horner’s syndrome is a nerve disorder that affects one side of the face, producing a cluster of signs. Elevated third eyelid, slightly drooping upper lid, a smaller pupil on that side, and sometimes warmth or flushing of the ear. Horner’s can follow a neck injury, middle ear infection, or may appear with no clear trigger. Cherry eye, which is prolapse of the gland inside the third eyelid, looks different. You see a pink or red mass bulging at the inner corner rather than a smooth membrane. Cherry eye is less common in cats than in dogs, but it does occur and usually requires surgical correction to prevent chronic dry eye.
Behavioral and Environmental Factors That Can Trigger Third Eyelid Visibility
Stress and fatigue sometimes cause mild, temporary elevation of the third eyelid. A cat who’s just moved to a new home, traveled in a carrier for hours, or endured a loud event like fireworks may show a slight membrane for 12 to 24 hours. This happens because stress can suppress appetite and water intake, leading to mild dehydration, or because the body’s stress response changes muscle tone and eye position. If your cat is eating, drinking, and acting normally otherwise, and the membrane is only barely visible, you can often wait a day to see if it resolves.
Sudden environmental changes can also trigger brief third eyelid visibility in sensitive cats. New pets, construction noise, even a change in litter box location. These cases resolve once the stressor is removed or your cat adjusts. Keep in mind that while behavioral causes exist, they’re diagnosis of exclusion. You should always rule out medical problems first, especially if the membrane stays up for more than 24 hours.
Common environmental triggers that may cause temporary third eyelid visibility:
• Relocation or travel. Car rides, plane trips, or moving to a new house.
• Introduction of a new pet or family member. Competition or anxiety over territory.
• Loud or unfamiliar noises. Fireworks, thunderstorms, home renovations.
• Changes in routine. New feeding schedule, different caregiver, rearranged furniture.
Symptoms That Indicate the Need for Veterinary Attention
A visible third eyelid paired with other symptoms almost always means your cat needs a vet exam. Squinting or holding one eye partly closed suggests pain. Excessive tearing or a watery discharge that leaves the fur below the eye damp and stained points to irritation or blocked tear ducts. Thick, colored discharge, yellow, green, or white, signals infection. Even clear discharge that persists for more than a day can mean an underlying problem like a scratched cornea or chronic conjunctivitis. If your cat paws at their face, rubs their eye on furniture, or shakes their head, they’re trying to relieve discomfort.
Fever, appetite loss, and behavioral withdrawal are systemic red flags. A cat who hides more than usual, stops grooming, or sleeps in unusual places may be masking illness. Check for a warm, dry nose and gums that feel tacky instead of slick. Loss of interest in food, especially if it lasts more than a day, can signal anything from dental pain to kidney disease. When a visible third eyelid appears alongside weight loss, vomiting, or diarrhea, the underlying cause is likely affecting the whole body. Parasites, organ disease, or infection.
Neurological symptoms demand emergency care. Disorientation, stumbling, head tilt, or pupils that are different sizes indicate a problem with the brain, nerves, or inner ear. A cat with Horner’s syndrome will have one small pupil, one elevated third eyelid, and possibly a drooping upper lid on the same side. This pattern suggests nerve damage or disruption, and while Horner’s itself isn’t painful, the cause can be serious. Ear infection, neck trauma, or tumor. Any sudden change in coordination or awareness, especially with third eyelid visibility, means you should seek care the same day.
| Symptom | What It Suggests |
|---|---|
| Thick yellow or green discharge | Bacterial eye infection requiring antibiotic treatment |
| Squinting, pawing, or head shaking | Pain from corneal ulcer, foreign body, or trauma |
| Fever and lethargy | Systemic infection or illness; dehydration likely |
| Both third eyelids raised with recent vomiting or diarrhea | Haws syndrome linked to gastrointestinal upset |
| One small pupil, drooping upper lid, and elevated third eyelid on one side | Horner’s syndrome; nerve damage or middle ear disease |
Diagnosis and What to Expect at the Vet
Your vet will start with a full physical exam, checking your cat’s temperature, hydration status, weight, and overall body condition. They’ll look at both eyes under bright light, comparing the two for symmetry, discharge, redness, and the extent of third eyelid visibility. The vet will gently lift the upper and lower lids to check for foreign objects, swelling, or signs of trauma. They may press lightly around the eye and face to test for pain or swelling in the tear ducts, sinuses, or jaw. If your cat has a fever or appears dehydrated, the vet will note dry gums, slow skin tent return, and may recommend immediate fluid therapy.
A fluorescein stain test is common when the vet suspects a corneal scratch or ulcer. The vet places a drop of orange dye on the eye, waits a moment, then rinses it with saline and shines a blue light. Any break in the corneal surface glows bright green. This test is quick, painless, and reveals injuries that are invisible to the naked eye. If the stain is positive, your cat will likely go home with antibiotic eye drops and pain medication. For suspected infections, the vet may take a swab of any discharge and send it for bacterial or fungal culture to guide antibiotic choice. Intraocular pressure measurement checks for glaucoma, though this is less common in cats than dogs.
Common diagnostic steps your vet may take:
- Physical and ocular exam. Check eye symmetry, pupil response, tear production, and signs of pain.
- Fluorescein stain test. Detect corneal ulcers or scratches that cause pain and third eyelid elevation.
- Parasite screening. Fecal sample or blood test to rule out tapeworms or other internal parasites.
- Temperature and hydration check. Confirm or rule out fever and dehydration as contributing factors.
- Blood work and imaging. If systemic illness is suspected, blood chemistry, complete blood count, and possibly X rays or ultrasound to evaluate organs and overall health.
Treatment depends entirely on the diagnosis. Eye infections typically respond to topical antibiotic or antiviral drops applied two to three times daily. Corneal ulcers require careful monitoring and sometimes protective Elizabethan collars to prevent pawing. Dehydration and fever are addressed with subcutaneous or intravenous fluids and treatment of the underlying cause. Antibiotics for infection, antiparasitics for worms, supportive care for gastrointestinal upset. Haws syndrome usually needs no direct treatment. It resolves as the GI issue improves. Cherry eye often requires surgical tacking to reposition the gland and prevent dry eye. Horner’s syndrome may resolve on its own, but the vet will investigate the cause, ear infection, trauma, or neurologic disease, and treat accordingly.
At Home Care and Monitoring While Waiting for a Vet Appointment
If you can’t reach a vet immediately but your cat is stable, focus on hydration and comfort. Offer fresh water in multiple bowls around the house. Some cats drink more from running water, so a pet fountain can help. You can also add a splash of low sodium chicken broth to water to make it more appealing. Check your cat’s gum color. Healthy gums are pink and moist. Press gently on the gum. The white spot should return to pink within one to two seconds. If it takes longer, your cat may be dehydrated, and you should prioritize getting fluids into them or seeking veterinary care sooner.
Keep your cat’s environment calm and quiet. Reduce stress by limiting loud noises, confining your cat to a quiet room if you have other pets, and maintaining a consistent feeding and litter routine. Watch for changes in behavior. Hiding more than usual, reduced grooming, or increased sleeping. Monitor both eyes several times a day and note whether the third eyelid is staying the same, getting worse, or improving. Take clear photos with good lighting so you can show your vet exactly what you see. If you notice new symptoms, discharge, squinting, lethargy, vomiting, write them down with the time and duration. This information helps your vet assess urgency and narrow down possible causes.
Don’t use over the counter human eye drops or ointments unless your vet specifically instructs you to. Many contain ingredients that are toxic to cats or that can worsen certain conditions. Saline rinse is generally safe for flushing debris, but anything medicated should come from a vet. Avoid touching or manipulating the third eyelid yourself. You can’t push it back into place, and handling the eye can introduce bacteria or cause further irritation. If your cat paws at their face, consider using a soft Elizabethan collar or a baby onesie with the legs cut short to prevent self trauma until you can get veterinary guidance.
Final Words
In the action, a visible third eyelid often signals something worth watching. Brief blinking while napping can be normal, but persistent or both eyes showing often means illness, pain, dehydration, infection, or injury.
We covered common causes, stress and environmental triggers, urgent warning signs, what your vet may check, and simple home care like keeping your cat hydrated and calm.
If you’re wondering what does it mean when a cat’s third eyelid is showing, use the red flags here: monitor mild cases, and seek vet care for sudden or severe signs. Most causes are treatable with prompt care.
FAQ
Q: Should I be worried if my cat’s third eyelid is showing?
A: A cat’s third eyelid showing is often normal briefly during sleep or waking, but persistent, bilateral, or accompanied by discharge, squinting, fever, appetite loss, or lethargy needs veterinary evaluation.
Q: How to treat the third eyelid in cats? How do vets treat a visible third eyelid?
A: Treating a visible third eyelid starts with keeping your cat hydrated, lowering stress, and avoiding human eye drops; a vet will exam, run tests, and may prescribe antibiotics, fluids, anti‑inflammatories, parasite treatment, or rarely surgery.
Q: Can stress cause a cat’s third eyelid to show?
A: Stress can cause a cat’s third eyelid to show temporarily, usually resolving within 12 to 24 hours; if it persists, shows discharge, or your cat acts unwell, contact your veterinarian.
