• Pink eye is a catch-all term for multiple kinds of conjunctivitis that may be caused by irritants, viruses, bacteria, or allergies.
• Conjunctivitis caused by bacteria or a virus often occurs along with a cold or symptoms of a respiratory infection.
• Conjunctivitis caused by allergies is linked to your environment, such as pollen or pet dander, rather than an infection.

Pink eye is a catch-all term for various types of conjunctivitis - inflammation or infection of the membrane that lines your eyelid and covers the white part of the eyeball. This can be caused by irritants, viruses, bacteria, or allergies.

Unlike viral or bacterial conjunctivitis, which is extremely contagious, allergic conjunctivitis is a reaction to your environment and cannot be spread.

"Pink eye is a wastebasket term, and it does not in and of itself tell a diagnosis," says Katheryn Colby, chair of the department of ophthalmology at NYU Langone Health. "When people think of pink eye, it's generally viral conjunctivitis. Allergic conjunctivitis is caused by an immune reaction to things in the environment like pollen or pet dander."

This article discusses the symptoms and causes of each condition associated with pink eye and ways to treat them.

What is viral and bacterial pink eye?

Conjunctivitis caused by bacteria or a virus often occurs along with a cold or symptoms of a respiratory infection, such as a sore throat. Wearing contact lenses that aren't cleaned properly can also cause bacterial conjunctivitis.

The most common symptoms are:

• Redness in one or both eyes
• Itchiness in one or both eyes
• A gritty feeling in one or both eyes
• A discharge in one or both eyes that forms a crust during the night that may prevent your eye or eyes from opening in the morning

A viral or bacterial infection may be diagnosed with a basic exam that involves a series of questions and a physical inspection from a doctor.

If the diagnosis is inconclusive, your doctor may use a slit lamp - an instrument with a microscope and a high-energy beam of light. If conjunctivitis lasts for more than two weeks after the initial diagnosis, your doctor may do an eye culture, which involves taking a sample of the cells on the inside of your eyelids with a cotton swab.

Viral and bacterial pink eye spread very easily from person to person, so if you or someone close to you has an infection be sure to wash your hands often with soap and water, avoid touching or rubbing your eyes, and don't share personal items like contacts or eye makeup.

What is allergic conjunctivitis?

Conjunctivitis caused by allergies is linked to your environment rather than an infection. Spring, summer, and fall eye allergies tend to be caused by trees, weed, grass, and flower pollen. Some people can have eye allergies all year round from dust, mold, and animal dander.

Symptoms vary from mild to severe, including:

• Itching
• Stinging or burning
• Tearing
• Pink and/or bloodshot eyes

If your doctor suspects allergic conjunctivitis, they may refer you to an allergist, who will review your medical history and symptoms and conduct tests for an eye allergy. However, in most cases, your primary care doctor can help you effectively manage this condition.

These tests might include an examination with a microscope or scraping the lining of the eyelid to look for white blood cells commonly present during allergic reactions.

Allergic conjunctivitis is not contagious.

How to treat bacterial or viral pink eye

Types of treatment vary based on what is causing the irritation. No drops or ointments can treat viral conjunctivitis. Like a common cold, the virus has to run its course, which may take up to two or three weeks.

Bacterial conjunctivitis is most often treated with antibiotic eye drops or ointments such as Bleph, Moxeza, or Romycin (erythromycin).

Although viral infections only heal with time, at-home remedies may aid the healing process and provide some relief. These include:

• Warm washcloth or compress to help reduce discharge buildup
• Cold compress to help relieve inflammation
• Avoid wearing contact lenses

The infection will usually clear up in 7 to 14 days.

How to treat allergies

Because eye allergies are caused by the environment, there are more options to help reduce them. Treatments include:

• Avoiding the allergen (i.e., keeping windows closed when the pollen count is high)
• Artificial tear drops help relieve eye allergies temporarily by washing allergens from the eye.
• Steroid eye drops
• Antihistamine eye drops, such as Pataday
• Allergy medications

As with other types of conjunctivitis, at-home remedies, include warm and cold compresses along with avoiding contact lenses.

The time it takes to get rid of eye allergies depends on exposure to the allergen and the effectiveness of the treatment, Colby says. Rubbing your eyes will only make it worse, she says.

"Allergen avoidance is the major treatment for that," Colby says. "If not, there are medicines that can be given to dampen the allergic response. Rubbing itself is like having a mosquito bite and scratching it, it makes the itching worse."

Insider's takeaway

Pink eye may be caused by bacteria, a virus, or allergies.

Though symptoms can be the same, causes and treatment options are very different. If you are experiencing itchiness, redness, or eye discharge, you should see your doctor.

"Regardless of what's causing it, it's good to avoid touching your eyes, and to wash your hands frequently," Colby says. "If symptoms are more than mild - loss of vision, severe pain - you'll want to be seen by an ophthalmologist."

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