Can conjunctivitis (pink eye) affect only one eye?

Yes, it is entirely possible for conjunctivitis, commonly known as pink eye, to affect only one eye initially. In many cases, symptoms may start in one eye, especially with viral conjunctivitis, which often begins in one eye and spreads to the other within days [4]. This can also occur with bacterial conjunctivitis or due to external irritants before the infection or inflammation spreads to the other eye.

Conjunctivitis is the swelling and inflammation of the transparent membrane that lines the eyelid and covers the white part of the eye [3]. Causes vary significantly; while some types, such as allergic conjunctivitis, tend to affect both eyes simultaneously due to exposure to the allergen, infectious types like viral and bacterial are highly contagious and can easily spread from one eye to the other or to other people [1].

Why might pink eye appear in only one eye?

When conjunctivitis appears in only one eye, it is often related to the type of infection or irritant. Viral conjunctivitis, the most common type, can begin in one eye and spread to the other [4]. Bacterial conjunctivitis may be accompanied by thick purulent discharge that causes the eyelids to stick together [4]. Because these types are highly contagious, it is very easy for them to spread to the other eye if a contaminated hand touches the healthy eye [1]. In contrast, external irritants such as dust, a foreign body, or chemical exposure to one eye may cause inflammation or irritation only in the exposed eye.

Characteristic symptoms requiring caution

Whether the inflammation affects one eye or both, the symptoms remain similar and require careful monitoring. Common signs you might notice include: clear redness in the white of the eye, swollen eyelids, itching, a burning sensation, or the feeling of a foreign body inside the eye. There may also be watery or purulent discharge (white, yellow, or green) that causes the eyelids to stick together upon waking [4]. Contact lens wearers may feel discomfort or notice that the lenses do not stay in place [4].

Prevention measures when affected in one eye

If your condition is limited to one eye, your primary goal is to prevent the spread of infection to the healthy eye and to others. Doctors recommend washing hands regularly with soap and water, especially before and after touching the infected eye or applying drops. Avoid sharing towels, pillows, or cosmetics with others entirely, and refrain from rubbing the eye, as this behavior is the primary cause of transmitting microbes from one eye to another or to others [3]. If you wear contact lenses, you must stop wearing them immediately, consult your doctor, and follow their instructions regarding when to resume lens use and how to handle them [3].

When does the condition require an immediate doctor visit?

While most cases of conjunctivitis resolve on their own, there are situations that require urgent medical care. See a doctor if you notice severe eye pain, unexplained intense redness, or if the inflammation significantly affects your vision and the vision does not improve after wiping away discharge. Also, if your immune system is weak, or if symptoms worsen and do not improve after a few days, you should seek professional medical evaluation [3]. To learn more about the nuances between infectious and non-infectious types, you can review our comprehensive guide on Conjunctivitis (Pink Eye): When is it contagious and when does it need antibiotics? (Arabic).

Medical references

• Choosing Wisely When It Comes to Eye Care: Antibiotics for Pink Eye
• Pink Eye
• Symptoms of Pink Eye | Conjunctivitis (Pink Eye) | CDC