A red, irritated eye is one of the most common reasons people seek same-day care, and one of the most common reasons antibiotic drops are prescribed unnecessarily.
Conjunctivitis comes in three main kinds, and they need three different things. Distinguishing them is usually possible from what the eye is doing rather than from how red it looks.
The discharge tells you more than the redness
All three types produce a red eye. What separates them is what comes out of it, whether it itches, and whether one eye or both are involved.
| Viral | Bacterial | Allergic | |
|---|---|---|---|
| Discharge | Watery or slightly mucousy | Thick, yellow or green pus | Watery and stringy |
| Main sensation | Gritty, burning | Gritty, sticky | Intense itching |
| Eyelids in the morning | Slightly crusted | Often stuck shut | Not stuck |
| Which eye | Starts in one, may spread | Often one, may spread | Both at once |
| Other symptoms | Often a cold or sore throat | Usually none | Sneezing, runny nose, other allergies |
| Contagious | Yes, highly | Yes | No |
| Usual treatment | Comfort measures and time | Antibiotic drops | Antihistamine drops, avoiding the trigger |
Intense itching is the single most useful pointer toward allergy. Eyelids genuinely stuck shut in the morning points toward bacterial. Watery discharge with a cold points toward viral.
One caveat about the table. It describes typical patterns rather than rules, and mixed pictures are common, particularly early on. Where symptoms are more than mild, or are not settling as expected, examination beats guesswork.
Viral is the most common
Most infectious conjunctivitis in adults is viral, frequently caused by the same viruses that cause ordinary colds. It typically starts in one eye and moves to the other a few days later.
It resolves on its own over one to two weeks, and antibiotic drops do nothing for it. They will not shorten it, will not stop it spreading, and can irritate the eye further.
This is the same reasoning set out in our article on antibiotic resistance: using an antibiotic where it cannot work carries cost without benefit.
Bacterial conjunctivitis
Bacterial conjunctivitis is less common in adults than viral, though it is relatively more common in children. The characteristic feature is thick pus that keeps returning through the day and glues the lids together overnight.
Antibiotic drops shorten it and are appropriate here. Even untreated, many mild cases resolve on their own, which is why prescribing is not automatic in every case.
Improvement should be evident within a day or two of starting drops. If it is not, go back rather than continuing to instill them, because the diagnosis may be wrong.
Allergic conjunctivitis often runs seasonally and alongside hay fever, and it can persist for weeks. It is the one kind where the answer is usually about avoiding a trigger rather than treating an infection.
It is extremely contagious
Viral conjunctivitis spreads readily, and people are usually infectious for as long as the eye is red and watering, which can be a week or more.
- Wash hands frequently, and avoid touching or rubbing the eyes
- Use your own towel, flannel and pillowcase, and wash them often
- Do not share eye makeup, and replace anything used while infected
- Do not wear contact lenses until the eye is completely settled
- Change pillowcases daily while symptomatic
- Stay away from work or school if advised, particularly in the first days
Discard any contact lenses, cases and solutions used while the eye was infected. Reusing them is a common route straight back into a second episode.
Newborns are the exception to every reassurance here. A red eye or discharge in a baby in the first weeks of life needs same-day assessment, because the causes and the consequences are different from those in older children and adults.
Makeup and lens habits are worth pausing entirely while symptoms last. Mascara and eyeliner used during an episode are a reliable route to reinfecting yourself a week later, and they are cheap to replace by comparison.
Treatment for each kind
Viral
Cool compresses, lubricating artificial tears, and time. Symptoms often worsen for the first three to five days before improving, which is expected rather than a sign of failure.
Bacterial
Antibiotic drops or ointment, which usually improve things within a day or two. Complete the course as prescribed, and clean the lids gently with cooled boiled water to remove crusting.
Allergic
Antihistamine or mast-cell stabilizing drops, cool compresses, and identifying and avoiding the trigger where possible. Rubbing makes it substantially worse.
Children are a common source of household spread, and conjunctivitis moves through schools and nurseries quickly. Separate towels and frequent hand washing are worth enforcing for a week or two even in people who are not yet symptomatic.
Most people can return to work or school once discharge has stopped and the eye is settling, though local policies vary. Ask rather than assume, particularly in healthcare, childcare and food handling roles.
When it is not simple conjunctivitis
Some red eyes are not conjunctivitis at all, and a few are sight-threatening. These features change the situation entirely.
Seek same-day eye assessment for pain in the eye rather than irritation, changes in vision, sensitivity to light, a foreign body sensation that will not clear, a red eye in a contact lens wearer, or a red eye after any injury.
- Moderate or severe pain, rather than grittiness
- Blurred vision, or any change in sight
- Marked sensitivity to light
- A red eye in someone who wears contact lenses
- Redness concentrated in a ring around the colored part of the eye
- A newborn with a red eye or discharge
- Symptoms that are not improving after a week, or are worsening
Contact lens wearers deserve particular caution. A red eye in a lens wearer can indicate a corneal infection, which is treated very differently and can threaten sight if it is missed.
Frequently asked questions
Do I need antibiotic drops for pink eye?
Only if it is bacterial, which is a minority of cases in adults. Thick yellow or green discharge with lids stuck shut in the morning points that way; watery discharge with a cold does not.
How long is pink eye contagious?
Viral conjunctivitis is usually contagious for as long as the eye is red and watering, often a week or more. Bacterial conjunctivitis is generally much less contagious once treatment has been running for about a day.
How do I know if it is allergy rather than infection?
Intense itching, both eyes affected at once, watery stringy discharge, and other allergy symptoms such as sneezing all point toward allergy. Allergic conjunctivitis is not contagious.
Can I wear my contact lenses?
Not until the eye is fully settled, and discard the lenses, case and solution used while it was infected. A red eye in a lens wearer should always be assessed, because it can indicate a corneal infection.
When should I worry about a red eye?
Genuine pain rather than irritation, any change in vision, marked light sensitivity, a red eye in a contact lens wearer, or redness after injury all need same-day assessment.
More about the specialty is on the infectious disease physician page, and the contact page explains how to reach the practice.
Sources and further reading: American Academy of Ophthalmology — Conjunctivitis: what is pink eye?.
This article is general health information, not medical advice, and it cannot account for your own history or medications. Discuss your situation with a qualified clinician before acting on anything you read here.