Pink Eye (Conjunctivitis)

Pink eye, known medically as conjunctivitis, is inflammation of the conjunctiva, the thin, clear membrane that lines the inside of the eyelids and covers the white part of the eye. When the conjunctiva becomes irritated or infected, its tiny blood vessels swell and become more visible, giving the eye its characteristic pink or red color. Conjunctivitis is not a single disease. It is an umbrella term for several different conditions that all cause this same type of inflammation—ranging from common viral and bacterial infections to allergic reactions and chemical irritation.

Pink eye is one of the most common eye conditions in the world. In the United States alone, approximately 6 million cases are diagnosed each year, making it the most frequently seen eye-related condition in emergency departments—accounting for nearly one-third of all eye-related emergency visits. Allergic conjunctivitis, the noninfectious form triggered by allergens, affects up to 40% of the North American population at some point. Most cases of pink eye are mild, resolve on their own or with simple treatment, and do not cause lasting harm. However, some forms—particularly certain infections in newborns and severe viral outbreaks—require prompt medical attention to prevent complications.

Doctors classify conjunctivitis by what caused it—an infection, an allergy, or a chemical or mechanical irritant. Identifying the type is important because each form is managed differently. The main types are:

• Viral conjunctivitis: the most common type of infectious pink eye worldwide. Most cases are caused by adenoviruses, which also cause the common cold. Adenoviral pink eye can appear in two forms: pharyngoconjunctival fever (PCF), which comes with sore throat and fever and is most common in children; and epidemic keratoconjunctivitis (EKC), the more severe form that can also affect the cornea and cause temporary vision disturbance. Other viruses that can cause conjunctivitis include herpes simplex virus (HSV), varicella-zoster virus (the virus that causes shingles), and enteroviruses. Viral conjunctivitis is highly contagious and spreads easily through direct contact with discharge from an infected eye or contaminated hands and surfaces.
• Bacterial conjunctivitis: caused by bacteria such as Staphylococcus, Haemophilus influenzae (most common in children), Streptococcus pneumoniae, and Moraxella catarrhalis. In sexually active adults, Neisseria gonorrhoeae and Chlamydia trachomatis can also infect the eye and cause a more severe form that requires immediate treatment. Bacterial pink eye is characterized by thick, pus-like discharge that often causes the eyelids to stick together overnight.
• Neonatal conjunctivitis (ophthalmia neonatorum): a form of bacterial conjunctivitis that can develop in a newborn during or shortly after delivery if the mother has a gonorrheal or chlamydial infection. This is considered a medical emergency because it can cause corneal scarring and permanent vision loss if not treated immediately. Routine eye drops or ointment are given to all newborns at birth to prevent this condition.
• Allergic conjunctivitis: a noninfectious form triggered by exposure to allergens such as pollen, pet dander, dust mites, and mold. It is extremely common, affecting up to 40% of the North American population. It causes itching, redness, and watery discharge and often occurs alongside other allergy symptoms such as sneezing and a runny nose. It is not contagious.
• Chemical or toxic conjunctivitis: caused by exposure to irritants such as chlorine in swimming pools, smoke, air pollution, chemical splashes, or preservatives in eye drops. Symptoms typically begin soon after exposure and resolve once the irritant is removed.
• Chronic conjunctivitis: pink eye that lasts longer than four weeks. It may result from a persistent low-grade bacterial infection, ongoing allergen exposure, dry eye disease, or an underlying inflammatory condition such as blepharitis (chronic eyelid inflammation).

Pink eye develops when something irritates or infects the conjunctiva, causing the blood vessels in the membrane to dilate and produce an inflammatory response. The most common causes are viruses and bacteria, though allergens and chemical irritants are also frequent culprits. In many cases—particularly with viral conjunctivitis—the pink eye begins in one eye and spreads to the other within days through hand-to-eye contact.

Viral causes are responsible for the majority of infectious conjunctivitis cases. Adenoviruses account for up to 90% of viral cases and spread easily in schools, daycare centers, and workplaces. Herpes simplex and varicella-zoster viruses can also infect the eye, typically causing a more persistent, sometimes painful form of conjunctivitis. Bacterial causes are most common in young children and are caused by germs that normally live on the skin or in the nose and throat, spreading to the eye by touch. Sexually transmitted infections such as gonorrhea and chlamydia can cause a particularly aggressive form of bacterial conjunctivitis in adults and are a leading cause of neonatal conjunctivitis in newborns. Specific causes include:

• Adenoviruses: the leading viral cause; spread through respiratory droplets and direct contact with infected secretions
• Herpes simplex virus (HSV): causes unilateral (one-eye) follicular conjunctivitis, often accompanied by small blisters on the eyelid
• Enteroviruses and coxsackievirus: associated with acute hemorrhagic conjunctivitis, which causes bleeding under the conjunctiva alongside the typical redness and tearing
• Staphylococcus, Haemophilus influenzae, and Streptococcus pneumoniae: the most common bacterial causes across all age groups
• Neisseria gonorrhoeae and Chlamydia trachomatis: causes of the most severe bacterial conjunctivitis in adults and newborns; require systemic antibiotic treatment
• Allergens (pollen, pet dander, dust, mold): trigger the immune system to release histamine and other chemicals that inflame the conjunctival surface
• Chemical irritants: chlorine, smoke, cleaning products, preservatives in eye drops, and other airborne or contact substances that can directly irritate or damage the conjunctiva

Anyone can develop pink eye, but certain circumstances and health factors make it more likely. Understanding these risk factors can help people take practical steps to reduce their exposure.

• Close contact with an infected person: Viral and bacterial conjunctivitis spreads easily in households, schools, daycare centers, and workplaces. Living with or caring for someone with pink eye significantly increases risk.
• Touching the eyes with unwashed hands: This is the single most common way infections spread to the eye.
• Contact lens wear: Contact lens wearers, especially those who sleep in lenses or who do not follow proper hygiene practices, face a higher risk of bacterial and viral conjunctivitis.
• Young age: Children in daycare and school settings are exposed to adenoviruses and bacteria frequently and are more likely to touch their eyes and faces.
• Seasonal allergies: People with hay fever, asthma, or eczema are at higher risk of allergic conjunctivitis, particularly during high-pollen seasons.
• Exposure to chemical irritants: People who swim frequently, work with chemicals, or live in high-pollution areas are more susceptible to chemical and toxic conjunctivitis.
• Sexually transmitted infections: Adults with untreated gonorrhea or chlamydia can develop conjunctivitis through hand-to-eye contact. Newborns are at risk during passage through an infected birth canal.
• Weakened immune system: Conditions or medications that suppress the immune system can increase susceptibility to both viral and bacterial eye infections.

There is no routine screening test for conjunctivitis. The condition is diagnosed when symptoms appear, and most cases are identified clinically by a doctor without laboratory testing. That said, when pink eye is caused by gonorrhea or chlamydia in a newborn, or when an outbreak occurs in a medical or institutional setting, laboratory cultures or swabs may be taken to identify the organism and determine the appropriate treatment.

Many cases of infectious conjunctivitis can be prevented with basic hygiene practices. Allergic conjunctivitis can be reduced by managing allergen exposure. The following steps are among the most effective at lowering risk:

• Wash hands frequently and thoroughly: Do this particularly after touching the face, before and after inserting contact lenses, and after being in public spaces during respiratory illness season.
• Do not touch or rub your eyes: especially with unwashed hands. The eye is a direct route for viruses and bacteria on the fingertips to cause infection.
• Do not share personal items: Avoid sharing towels, washcloths, pillowcases, makeup, or eye drops with others, even family members.
• Follow proper contact lens hygiene: Clean and store lenses only with approved solutions. Replace lenses and cases on schedule. Never sleep in lenses unless specifically prescribed for overnight wear.
• Stay home when infected: People with viral or bacterial conjunctivitis should avoid school, work, and public spaces until symptoms have resolved and, if treated, until at least 24 hours after starting antibiotic drops (for bacterial infection).
• Manage allergen exposure: Keep windows closed during high-pollen days, use air purifiers, shower after outdoor activities, and wash bedding frequently. Over-the-counter or prescription allergy medicines can reduce allergic conjunctivitis symptoms significantly.
• Prenatal sexually transmitted infection (STI) screening and treatment: Pregnant women should be screened and treated for gonorrhea and chlamydia to prevent neonatal conjunctivitis. Routine antibiotic eye drops or ointment given at birth provides an additional layer of protection for all newborns.

The hallmark sign of all forms of conjunctivitis is redness or pinkness in the white of the eye, caused by swollen blood vessels in the conjunctiva. This redness is almost always accompanied by some form of discharge or tearing and varying degrees of discomfort. The specific pattern of symptoms can help identify the type of conjunctivitis, which guides treatment decisions.

Common signs and symptoms of pink eye include:

• Pink or red color in the white of one or both eyes: This is the most recognizable sign; caused by dilated and inflamed blood vessels in the conjunctiva.
• Discharge from the eye: The type of discharge differs by cause. Viral conjunctivitis typically produces a clear or slightly white, watery discharge. Bacterial conjunctivitis produces thick, yellow-green, pus-like discharge that can cause the eyelids to stick together, especially after sleep. Allergic conjunctivitis produces a thin, watery or slightly mucousy discharge.
• Itching: This is a prominent feature of allergic conjunctivitis; typically less intense in viral and bacterial forms.
• Burning or stinging: This is particularly common with chemical or toxic conjunctivitis and with viral forms.
• Increased tearing: The eye produces more tears than usual in response to irritation.
• Crusting around the eyelids or lashes: This is most noticeable in the morning with bacterial conjunctivitis, where dried discharge forms a crust that can seal the eyelids.
• Swelling of the eyelids: This presents as mild puffiness of the upper and lower lids from inflammation.
• Sensitivity to light (photophobia): This is more common in viral conjunctivitis, especially epidemic keratoconjunctivitis (EKC), where the cornea can also be affected.
• Gritty or foreign body sensation: This is a feeling that something is stuck in the eye.
• Blurred vision: usually mild and temporary in most forms of conjunctivitis, typically clearing with blinking. Persistent blurring may signal corneal involvement and requires prompt evaluation.
• Swollen lymph node in front of the ear: A small, tender bump in front of the ear (preauricular lymphadenopathy) is characteristic of adenoviral and herpes conjunctivitis and helps distinguish these from bacterial forms.
• Sore throat and fever: When conjunctivitis is part of pharyngoconjunctival fever, throat soreness and mild fever accompany the eye symptoms, particularly in children.

Most cases of pink eye are diagnosed by a doctor based on symptoms and a physical examination of the eye. More than 80% of conjunctivitis cases are diagnosed by primary care providers—including internists, family medicine physicians, and pediatricians—rather than by eye specialists. In most straightforward cases, laboratory tests are not needed. However, certain presentations—such as conjunctivitis in a newborn, suspected gonorrheal or chlamydial infection, severe or worsening symptoms, or an outbreak in a group setting—warrant laboratory testing to identify the organism and guide treatment. The following tests and techniques are used:

• Slit-lamp examination: An ophthalmologist uses a magnifying microscope with a bright light to examine the surface of the eye and eyelid lining in detail. This allows the doctor to assess the type and severity of inflammation, check for corneal involvement, and identify features such as follicles (small raised bumps on the inner eyelid surface, common in viral infections), papillae (larger bumps with a central blood vessel, more common in allergic and bacterial forms), or membranes on the conjunctival surface.
• Conjunctival swab and culture: A swab of the discharge or inner eyelid surface is sent to a laboratory to grow and identify bacteria. This is most important when gonorrhea, chlamydia, or antibiotic-resistant bacteria are suspected, and in all cases of neonatal conjunctivitis.
• Polymerase chain reaction (PCR) testing: A molecular test can rapidly and accurately identify adenovirus, herpes simplex virus, chlamydia, and other organisms from a conjunctival swab. It is more sensitive than culture for viral and atypical bacterial causes.
• Gram stain: A quick laboratory test performed on a swab sample can identify bacteria under a microscope within minutes. It can immediately confirm a gonorrheal infection, which is a medical emergency.
• Allergy testing: For patients with suspected allergic conjunctivitis that does not respond to standard treatment, skin prick testing or blood allergy testing (radioallergosorbent—RAST) can identify specific allergen triggers.
• Complete medical and exposure history: The doctor will ask about the onset and pattern of symptoms, any discharge type, recent illness or sick contacts, contact lens use, current medications and eye drops, known allergies, and potential chemical exposures. This history is often the most useful diagnostic tool for distinguishing viral from bacterial from allergic conjunctivitis without laboratory testing.

The treatment for pink eye depends entirely on its cause. Not all forms of conjunctivitis require prescription medication—in fact, most viral cases clear on their own without any treatment. The key is identifying the type correctly so that the right care is given and unnecessary antibiotic use is avoided. Your doctor will guide treatment based on the symptoms, the likely cause, and whether any complications are present.

Viral conjunctivitis—including the most common adenoviral form—is self-limited, meaning it resolves on its own without antibiotics. Treatment focuses on keeping the eye comfortable while the immune system fights the infection. Applying a clean, cold, damp cloth to the closed eye several times a day can relieve redness and swelling. Preservative-free artificial tears help rinse away discharge and soothe the eye’s surface. Because viral conjunctivitis is highly contagious, careful hand washing and avoiding shared towels or pillowcases are essential. Most cases resolve within one to two weeks. The more severe epidemic keratoconjunctivitis (EKC) may take longer. If corneal involvement produces visual disturbance, a short course of anti-inflammatory eye drops prescribed by an ophthalmologist may be used. When herpes simplex or varicella-zoster virus is the cause, antiviral eye drops (such as ganciclovir 0.15% gel Zirgan®) or oral antiviral medicines (such as acyclovir or valacyclovir) are prescribed to shorten the course and prevent recurrence.

Bacterial conjunctivitis in otherwise healthy children and adults is often self-limiting and may resolve within one to two weeks without antibiotics. However, antibiotic eye drops or ointment are commonly prescribed to shorten the duration, reduce contagiousness more quickly, and lower the small risk of the infection spreading deeper into the eye. Topical fluoroquinolone drops (such as moxifloxacin or ciprofloxacin), polymyxin B/trimethoprim drops, or erythromycin ointment are commonly used. Bacterial conjunctivitis caused by gonorrhea or chlamydia always requires immediate systemic (oral or injected) antibiotics—topical drops alone are not sufficient for these infections. Neonatal conjunctivitis is treated urgently, with the specific antibiotic chosen based on laboratory identification of the causative organism. Chlamydial neonatal conjunctivitis requires oral erythromycin to prevent the infection from spreading to the lungs. All newborns receive prophylactic antibiotic ointment (typically erythromycin) in both eyes at delivery as a standard precaution against neonatal infection.

Allergic conjunctivitis is managed by reducing allergen exposure and controlling the immune response. Over-the-counter antihistamine and mast cell stabilizer combination eye drops—such as olopatadine (Pataday®) and ketotifen (Zaditor®)—are effective first-line treatments and are available without a prescription. Prescription-strength versions provide more sustained relief. Cold compresses applied to the closed eyes help reduce itching and swelling quickly. Oral antihistamines may reduce allergy symptoms throughout the body, including the eyes, but they can also dry the eyes as a side effect. For severe or chronic allergic conjunctivitis that does not respond to antihistamine drops, your doctor may prescribe topical corticosteroid (steroid) eye drops for short-term use, or topical immunomodulatory agents such as cyclosporine. Chemical or toxic conjunctivitis is treated by removing the irritant—this may mean rinsing the eye thoroughly with clean water or saline immediately after exposure—and using preservative-free artificial tears to support healing of the surface.

For most people, a bout of pink eye is an uncomfortable but brief experience that resolves fully with proper care and hygiene. Viral cases typically clear up within one to two weeks, and bacterial cases often improve within a few days of starting antibiotic drops. Allergic conjunctivitis is the type most likely to become a recurring or chronic issue, particularly during allergy seasons or in people with persistent allergen exposure at home or work. For those with chronic allergic conjunctivitis, working with an allergist or ophthalmologist to identify triggers and establish a consistent management routine can make a meaningful difference in daily comfort. It is important to call your doctor if pink eye symptoms worsen significantly, if your vision changes, if light sensitivity becomes severe, or if symptoms do not begin to improve after a week—these can occasionally be signs of a more serious eye condition that needs closer evaluation.

To further your understanding of your diagnosis and to contribute to cutting-edge research, consider participating in a clinical trial so clinicians and scientists can learn more about causes, symptoms, treatment, and prevention of conjunctivitis and related disorders. Clinical research uses human volunteers to help researchers learn more about a disorder and perhaps find better ways to safely detect, treat, or prevent disease.

All types of volunteers are needed—those who are healthy or may have an illness or disease—of all different ages, sexes, races, and ethnicities to ensure that study results apply to as many people as possible, and that treatments will be safe and effective for everyone who will use them.

To learn more about clinical trials and find studies that may be right for you, visit National Institutes of Health (NIH) Clinical Research Trials and You at www.nih.gov/health-information/nih-clinical-research-trials-you and ClinicalTrials.gov at www.clinicaltrials.gov to search active studies by condition, location, and age group.