Conjunctivitis, also known as “pink eye,” is the inflammation or infection of the conjunctiva, the thin, clear tissue that covers the white part of the eye and lines the inside of the eyelids. It commonly causes redness, irritation, itching or burning, tearing, and discharge from the eye. The discharge may be watery or thick and pus-like, depending on the cause. Conjunctivitis can affect one or both eyes and may range from a mild condition that clears up on its own to a more persistent infection that requires medical treatment.
This condition can be caused by viruses or bacteria (infections), allergic reactions (such as to pollen or pet dander), or irritants like smoke, chemicals, or air pollution. Viral and bacterial conjunctivitis are contagious and can spread easily through direct contact or by touching contaminated objects and surfaces. Identifying the cause is important because treatment differs between infectious and non-infectious types.
Conjunctivitis is very common in people of all ages and can appear on its own or alongside conditions such as colds, allergies, or skin disorders. Because it spreads easily in crowded environments, understanding the symptoms, how it is transmitted, and how to prevent it helps reduce the risk of infection and protects others.
The conjunctiva helps keep the eye moist by producing mucus and contributing to the tear film, which washes away dust and small particles. It also acts as a protective barrier against germs and irritants. Beneath it lies the sclera (the white part of the eye), which provides structure, and the eyelids contain glands that release oils to keep tears from drying too quickly. These structures work together to protect the eye’s surface and maintain clear, comfortable vision.
Conjunctivitis may be short-term (acute) or long-lasting (chronic) and is commonly called “pink eye” because the inflammation causes the blood vessels in the conjunctiva to become more visible, giving the eye a reddish or pink appearance.
Types of Conjunctivitis
There are three main types:
- Viral Conjunctivitis: Caused by viruses, often linked to colds; highly contagious.
- Bacterial Conjunctivitis: Results from bacterial infections; treated with antibiotics.
- Allergic Conjunctivitis: Triggered by allergens such as pollen or pet dander; causes itching.
Each type shares similar symptoms but differs in cause, contagiousness, and treatment methods.
Causes of Conjunctivitis
Conjunctivitis results from different sources including infections and allergic reactions. Each type involves distinct triggers and symptoms that determine treatment approaches.
Bacterial Conjunctivitis
Bacterial conjunctivitis is caused by the introduction of harmful bacteria into the conjunctiva. Common bacterial organisms include Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae, although other species may be implicated depending on age, environment, and general health. In newborns, for instance, Neisseria gonorrhoeae or Chlamydia trachomatis can cause a severe form of conjunctivitis acquired during childbirth.
This type of conjunctivitis often begins in one eye but can quickly spread to the other if proper hygiene is not maintained. It typically produces thick, sticky, or pus-like (purulent) discharge that may cause the eyelids to stick together, especially after sleep. Transmission commonly occurs through direct contact with infected eye secretions, touching contaminated surfaces, or using shared personal items like towels or eye makeup. Poor hand hygiene increases the risk of spread. Bacterial conjunctivitis may resolve on its own in mild cases, but antibiotic eye drops or ointments are frequently prescribed to shorten the duration of symptoms and reduce complications.
Viral Conjunctivitis
Viral conjunctivitis is most often caused by adenoviruses, which are the same group of viruses responsible for many respiratory infections, including the common cold and sore throat. Less commonly, viral conjunctivitis can be associated with systemic viral illnesses such as measles, varicella (chickenpox), or herpes simplex virus. This form of conjunctivitis is highly contagious and may spread through hand-to-eye contact after touching infected respiratory droplets, as well as through shared objects, towels, or contact lenses.
Symptoms of viral conjunctivitis typically include watery discharge, redness, tearing, and a gritty or “foreign body” sensation in the eye. It frequently occurs alongside cold-like symptoms such as a runny nose, coughing, or sore throat. Because antibiotics do not treat viral infections, management is usually supportive, focusing on symptom relief through cool compresses, artificial tears, and strict hygiene to limit spread. In most cases, the infection resolves within one to two weeks.
Allergic Conjunctivitis
Allergic conjunctivitis occurs when the immune system overreacts to harmless substances (allergens) such as pollen, dust mites, mold spores, or pet dander. Unlike bacterial or viral conjunctivitis, it is not contagious and cannot be passed from one person to another. It commonly affects both eyes at the same time and is more frequently seen in individuals with a history of allergic conditions such as asthma, eczema, or hay fever.
Symptoms of allergic conjunctivitis include intense itching, tearing, redness, and swelling of the eyelids. The discharge is usually watery rather than pus-like, since the irritation is caused by inflammation rather than infection. Seasonal allergic conjunctivitis occurs at specific times of the year, particularly during high pollen seasons, whereas perennial allergic conjunctivitis occurs year-round due to indoor allergens such as dust or pet hair. Treatment typically includes avoiding known triggers, using antihistamine or anti-inflammatory eye drops, and in more persistent cases, medical therapies that help regulate the immune response.
Symptoms and Signs
Conjunctivitis presents with visible changes and discomfort in the eyes that can vary by cause. It typically affects one or both eyes and may produce symptoms that interfere with daily activities. Common signs include alterations in eye appearance and sensations around the eyelids.
Redness and Irritation
The most noticeable symptom of conjunctivitis is redness in the white part of the eye. This redness results from inflammation and dilation of blood vessels in the conjunctiva. Patients often report a gritty or burning feeling.
Irritation typically worsens with exposure to wind, smoke, or bright light. The sensation of itchiness or a foreign body in the eye is common, though severity varies. Redness may spread from one eye to the other if caused by an infection.
Eye Discharge
Discharge differs based on the type of conjunctivitis. Bacterial infections usually produce a thick, yellow or green pus-like discharge. This can cause eyelids to stick together, especially after sleeping.
Viral conjunctivitis often leads to a watery or clear discharge. Allergic conjunctivitis usually triggers thin, stringy mucus. The amount and consistency of discharge are key indicators in distinguishing causes.
Swelling and Tearing
Swelling of the conjunctiva and eyelids often accompanies redness and discharge. It causes puffiness and may restrict eyelid movement, adding to discomfort. Swelling is usually more pronounced in bacterial and allergic types.
Excessive tearing occurs as a response to irritation and attempts to flush out allergens or infectious agents. Tearing is nearly constant in allergies but intermittent in infections. Both swelling and tearing contribute to blurred vision temporarily.
Diagnosis of Conjunctivitis
Diagnosis involves a detailed clinical evaluation supported by specific tests when necessary. Careful assessment distinguishes conjunctivitis from other ocular conditions and identifies its cause. The process relies on observable signs and targeted investigations.
Physical Examination
The physician examines the eye for redness, discharge, swelling, and irritation. They assess the type of discharge—watery or purulent—to help differentiate viral, bacterial, or allergic conjunctivitis. Lid swelling and presence of follicles or papillae on the conjunctiva are also noted.
Visual acuity is checked to rule out involvement of deeper eye structures. The doctor inspects both eyes and asks about symptom duration, exposure to irritants or allergens, and presence of systemic symptoms like fever. These details guide diagnosis and treatment.
Laboratory Testing
Lab tests are used when the cause is unclear or symptoms persist despite treatment. A conjunctival swab may be collected to identify bacterial or viral pathogens through culture or polymerase chain reaction (PCR) testing.
Allergy testing may be employed if allergic conjunctivitis is suspected to confirm specific triggers. In cases with suspected chlamydial or gonococcal infection, advanced testing is essential for targeted therapy. Lab results help confirm diagnosis and determine the appropriate treatment approach.
Treatment Options
Antibiotic Therapy
Antibiotic treatment is primarily used for bacterial conjunctivitis. Antibiotic eye drops or ointments help eliminate the infecting bacteria and shorten the duration of symptoms. Commonly prescribed medications include erythromycin ointment and eye drops containing tobramycin or ciprofloxacin. These agents work by either killing bacteria or preventing their growth, allowing the body to clear the infection more efficiently.
Symptoms typically begin to improve within 24 to 72 hours of initiating treatment. However, it is important for patients to complete the full course of antibiotics even if the eye begins to feel better early, as stopping too soon may allow bacteria to survive and lead to recurrence or antibiotic resistance. Antibiotics are not useful for viral or allergic conjunctivitis, and their unnecessary use can contribute to the development of resistant bacterial strains. For this reason, accurate diagnosis by a healthcare provider is strongly recommended before starting therapy.
Antiviral Medications
Most cases of viral conjunctivitis are caused by adenoviruses and do not require antiviral drugs, as the body’s immune system clears the infection over time. Supportive care such as applying cool compresses, using artificial tears, and practicing good hygiene helps relieve symptoms while the infection resolves.
However, antiviral medications are necessary when conjunctivitis is caused by viruses such as herpes simplex virus (HSV) or varicella-zoster virus. In these cases, topical antiviral ointments like acyclovir or systemic (oral) antiviral drugs may be prescribed to reduce viral replication, control symptoms, and prevent complications. Because HSV-related conjunctivitis can lead to corneal damage and long-term vision problems if not promptly treated, early medical evaluation is crucial. Antiviral therapy does not benefit allergic or bacterial conjunctivitis and should only be used when a viral cause is confirmed or strongly suspected.
Allergy Management
Allergic conjunctivitis is treated by targeting the immune response that triggers eye irritation. The first-line therapy typically includes antihistamine or mast cell stabilizer eye drops, such as olopatadine, ketotifen, or azelastine. These medications reduce itching, redness, and swelling by blocking the release of histamine, the chemical responsible for allergic symptoms or by preventing its release altogether.
In individuals with more persistent or systemic allergic symptoms, oral antihistamines may be added to improve symptom control. Avoiding known allergens such as pollen, dust mites, pet dander, or mold, is also an important part of management. For patients with severe or long-lasting inflammation that does not respond to standard treatment, a short course of topical corticosteroids may be prescribed under close medical supervision.
These medications are effective but must be used cautiously, as long-term or unsupervised use can lead to side effects such as increased eye pressure or cataract formation.
Prevention Strategies
- Good personal hygiene is the most effective way to prevent the spread of conjunctivitis.
- Frequent handwashing with soap and clean water is essential, especially before touching the eyes, face, or contact lenses.
- Handwashing removes viruses, bacteria, and allergens that may transfer from the hands to the eye’s surface.
- Avoid sharing personal items such as towels, washcloths, pillowcases, cosmetics, or eye makeup, as these can harbor infectious particles.
- Contact lens wearers should clean and store lenses properly using approved solutions, not tap water.
- Lenses should be replaced as recommended, and sleeping in contact lenses without approval increases irritation and infection risk.
- Avoid rubbing or touching the eyes with unwashed hands to prevent introducing pathogens or worsening inflammation.
- During infection, replace or thoroughly clean items like makeup applicators, mascara brushes, and contact lens cases to prevent reinfection.
- Refrain from using cosmetic products until all symptoms have resolved.
Environmental Controls
Environmental hygiene is equally important, particularly in shared or communal settings. Frequently touched surfaces such as doorknobs, light switches, countertops, handrails, remote controls, and shared electronic devices should be cleaned and disinfected regularly to reduce the spread of bacteria and viruses. In households with an infected person, dedicating separate towels, linens, and bedding reduces cross-contamination. These items should be washed in hot water with detergent to eliminate pathogens effectively.
Using disposable tissues and discarding them immediately after use helps prevent the transfer of infectious secretions to surfaces or other individuals. Maintaining good ventilation reduces humidity and discourages the growth of microorganisms that thrive in moist environments. In institutional environments such as schools, daycare centers, and clinics, temporarily isolating infected individuals or advising them to stay home until symptoms improve is an important public health strategy that helps control outbreaks.
When combined, these personal and environmental measures significantly reduce the likelihood of transmission and contribute to overall ocular health.
Complications of Conjunctivitis
Conjunctivitis can lead to persistent symptoms or affect the eye’s normal function. Some complications result in prolonged discomfort, while others may risk vision clarity.
Chronic Conjunctivitis
Chronic conjunctivitis refers to inflammation of the conjunctiva that lasts longer than four weeks. It may develop when an initial case of conjunctivitis is not adequately treated or when the eyes remain continuously exposed to irritants such as smoke, air pollution, or allergenic substances. Persistent infections involving bacteria, viruses, or underlying eyelid conditions such as blepharitis or meibomian gland dysfunction can also contribute to chronic inflammation.
Individuals with chronic conjunctivitis often experience continuous redness, mucoid discharge, itching or burning sensations, and a persistent gritty feeling in the eye. Over time, long-standing irritation may thicken or scar the conjunctival tissue, reducing its ability to lubricate and protect the ocular surface. If not addressed, chronic conjunctivitis can also increase susceptibility to secondary infections and may impair tear film stability, further worsening symptoms.
Vision Impairment
Vision impairment from conjunctivitis is uncommon but can occur in severe, untreated, or complicated cases, particularly when the cornea becomes involved. The cornea is the transparent, dome-shaped front surface of the eye responsible for focusing light. Prolonged or intense inflammation from conjunctivitis can disrupt the corneal surface, resulting in corneal ulcers, erosions, or scarring.
Corneal involvement is more likely in cases caused by virulent pathogens such as herpes simplex virus or bacteria capable of penetrating the ocular surface. Symptoms suggesting corneal complications include sharp eye pain, increased light sensitivity (photophobia), blurred or reduced vision, and a sensation of a foreign body in the eye. Without prompt treatment, corneal ulcers can leave permanent scars that interfere with visual clarity.
Prognosis and Recovery
Recovery from conjunctivitis varies depending on the cause but generally results in full resolution without lasting damage. Some cases resolve quickly, while others may take longer and require ongoing management.
Duration of Illness
The duration depends on whether the conjunctivitis is viral, bacterial, or allergic.
- Viral conjunctivitis usually lasts 7 to 14 days. It often improves without treatment but may persist if caused by certain viruses like adenovirus.
- Bacterial conjunctivitis typically resolves within 7 to 10 days, especially with antibiotic treatment which can shorten its course to 2-5 days.
- Allergic conjunctivitis can last as long as the allergen is present, which may be weeks or longer if untreated.
Symptom severity usually peaks early and then gradually declines. Patients with proper hygiene and timely treatment tend to recover faster.
Long-Term Outcomes
Most cases of conjunctivitis clear without permanent damage to the eye.
Chronic or recurrent cases may occur in allergic or irritant conjunctivitis if triggers are not avoided.
Complications like corneal ulcers or scarring are rare and mainly happen if the infection is severe or treatment is delayed.
Visual impairment is uncommon but may occur temporarily in severe cases due to inflammation or discharge. The risk of lasting sequelae increases with inappropriate treatment or underlying eye conditions.
Conjunctivitis in Special Populations
Children
Children are particularly vulnerable to conjunctivitis because of their frequent hand-to-eye contact, limited awareness of hygiene practices, and close interaction with peers in environments such as schools and daycare centers. Bacterial conjunctivitis is the most common type in this age group and typically presents with thick, sticky, purulent discharge that may cause the eyelids to stick together after sleep. Children may also rub their eyes frequently, which worsens irritation and can further spread infection.
Viral conjunctivitis is also frequently observed in children, especially when respiratory infections such as the common cold or adenovirus outbreaks are circulating in group settings. Symptoms tend to include watery discharge, burning sensations, and increased sensitivity to light (photophobia). Because viral strains are highly contagious, entire classrooms or households may be affected.
Immunocompromised Individuals
Immunocompromised individuals such as patients undergoing chemotherapy, individuals with uncontrolled diabetes, organ transplant recipients on long-term immunosuppressants, or those living with HIV/AIDS are at a much higher risk of developing severe, chronic, or atypical forms of conjunctivitis. In these patients, the natural immune defenses that typically clear infections are weakened, allowing otherwise mild pathogens to cause aggressive or persistent inflammation.
Unlike the general population where conjunctivitis is most often viral or bacterial, immunocompromised patients may develop conjunctivitis due to opportunistic pathogens, including fungi, cytomegalovirus (particularly in advanced HIV), parasites, or rare bacterial species not typically pathogenic in healthy individuals. These infections tend to progress more rapidly and may spread deeper into ocular tissues, increasing the risk of keratitis (inflammation of the cornea), corneal ulceration, and potential vision loss.
When to Seek Medical Attention
Medical attention is necessary if symptoms of conjunctivitis worsen or do not improve within a week. Persistent redness, pain, or discharge can indicate a more serious condition requiring professional evaluation.
If a person experiences significant eye pain, vision changes, or sensitivity to light, they should seek immediate care. These symptoms may signal complications or other eye disorders.
Urgent consultation is recommended when:
- Thick, colored discharge persists
- Swelling around the eye increases
- Both eyes become affected quickly
- Symptoms occur after eye injury or contact with chemicals
Infants, young children, and individuals with weakened immune systems should also see a healthcare provider early. Timely diagnosis can prevent complications and guide appropriate treatment.
If conjunctivitis is suspected to be caused by bacteria, a doctor may prescribe antibiotics. Viral and allergic conjunctivitis usually resolve without medication but still warrant assessment if severe.
In summary, seeking medical attention depends on symptom severity, duration, and associated risk factors. A healthcare professional can provide accurate diagnosis and management advice.