Conjunctivitis

Conjunctivitis is inflammation of the conjunctiva, the pink membrane that lines the inside of the eyelids and covers the white part of the eye. This tissue protects the eye from foreign objects and microorganisms and helps keep tears spread evenly over the surface. When it gets irritated or infected, it swells up and turns red, which is why you'll often hear it called pink eye in both pets and people.

You'll usually notice it as a red or swollen rim around the eye, along with some combination of squinting, blinking more than usual, or your pet rubbing at their face. Discharge often follows, ranging from cloudy to yellow or greenish, and dogs and cats with conjunctivitis often have redness and swelling around the eye too. As a rough guide, green or yellow discharge tends to point toward a bacterial cause, while clear or whitish discharge is more often linked to allergies or a bit of debris in the eye. The condition can affect one eye or both, and both eyes are more commonly affected, though it can show up in just one.

What's actually driving the inflammation differs quite a bit between species. In dogs, allergies are a frequent culprit, with pollen, dust, and other everyday irritants setting off a reaction, though bacterial infections and physical irritants like grass seeds or eyelash problems play a role too. Cats are a different story: most canine conjunctivitis happens secondary to an underlying irritant, while in cats it's usually caused by primary pathogens, mainly feline herpesvirus (FHV-1) and Chlamydia felis. These feline infections spread easily between cats, especially in shelters or multi-cat households, and once a cat is infected with FHV-1 it carries the virus for life, with flare-ups possible whenever its immune system is under stress.

A few signs mean it's worth getting seen sooner rather than later:

• Thick discharge that glues the eyelids shut, especially in kittens or puppies
• One eye that looks noticeably more swollen, red, or painful than the other
• Squinting alongside cloudiness or a visible scratch on the eye's surface, which could mean a corneal ulcer rather than simple conjunctivitis
• Conjunctivitis paired with sneezing, coughing, or nasal discharge, which in cats often points to a respiratory virus
• Symptoms lasting more than a few days or coming back repeatedly

The reason a vet check matters even for something that looks minor is that although the usual causes of conjunctivitis are common and mild, more serious eye diseases or even systemic illness can start out looking exactly the same, so a proper clinical assessment matters for both eye health and overall wellbeing. A vet can also tell the difference between a scratch, allergy, and infection using simple tests like eye staining, which changes the treatment completely since steroid drops that help allergies can actually worsen an ulcer. Treatment itself is usually straightforward once the cause is clear, typically drops or ointment, sometimes paired with an oral antiviral or antibiotic for the infections that need it.