Allergic conjunctivitis is an allergic reaction of the eye to an allergen such as pollen, mold or dander. It involves an inflammation of the clear membrane that covers the white of the eye and can result in itching, burning, and redness in the eye. Swollen eyelids, watery eyes and eye discharge also are symptoms of allergic conjunctivitis.

There are several forms of allergic conjunctivitis:

• Seasonal allergic conjunctivitis (SAC). Flares up on a seasonal basis and is frequently associated with allergic rhinitis.
  
  
• Perennial allergic conjunctivitis (PAC). Symptoms manifest themselves year-round.
  
  
• Vernal conjunctivitis. More common in the spring and fall, afflicts more males than females, and can lead to vision loss. Vernal conjunctivitis exists in both allergic and non-allergic forms.
  
  
• Atopic keratoconjunctivitis. A type of allergic conjunctivitis that is associated with atopic dermatitis of the eyelids and face.

Pollen is the primary allergen that triggers allergic conjunctivitis. Tree and grass pollens tend to trigger the condition in spring and early summer, while weed pollens tend to be the main culprit in the summer and early fall. Allergic conjunctivitis also can result from contact with dust and fungus spores, or from coming into contact with certain animal and vegetable proteins.

Frequently, those who suffer from allergic conjunctivitis also have a family history of conditions such as allergic rhinitis, asthma or eczema.

Allergic conjunctivitis is just one form of the disease. There also are other forms of conjunctivitis, such as bacterial conjunctivitis, which is caused by bacteria, and viral conjunctivitis, which is caused by viruses.

Allergic conjunctivitis is an inflammation of the clear layer of skin that covers the eye and is triggered by an allergic reaction. It occurs when the eye comes into contact with an allergen and reacts by releasing histamine. This causes the blood vessels of the conjunctiva (a membrane that covers the white of the eye and inside of eyelids) to enlarge.

This is quickly followed by eye-related symptoms such as reddening of the eye, an itching sensation and tearing. These symptoms usually are accompanied by nasal symptoms, such as congestion, sneezing and an itchy nose. While non-allergic conjunctivitis often affects only one eye, allergic conjunctivitis usually affects both eyes at once.

There are several categories of allergic conjunctivitis:

• Seasonal allergic conjunctivitis (SAC). The most common form of allergic conjunctivitis, it occurs seasonally as plants pollinate and produce airborne allergens such as grass, tree and weed pollens, and molds. It is frequently a consequence of allergic rhinitis (hay fever) and is sometimes referred to as “hay fever conjunctivitis.”
• Perennial allergic conjunctivitis (PAC). A less common form of allergic conjunctivitis in which symptoms are experienced all year long. The main allergens involved in PAC are animal dander, dust mites and feathers. Though symptoms can occur throughout the year and usually are milder than those of SAC, they may worsen seasonally.
• Vernal conjunctivitis. A chronic form of conjunctivitis that occurs most often in the spring and fall. It has the potential to permanently damage vision and is much more likely to occur in males than in females, particularly those younger than 10 who also have a history of allergies. Vernal conjunctivitis exists in both allergic and non-allergic forms. Children often outgrow the condition by the time they reach early adulthood.
• Atopic keratoconjunctivitis. A type of allergic conjunctivitis that is associated with atopic dermatitis of the eyelids and face. Symptoms include redness, itchiness, burning, tearing, stringy or ropy discharge and swelling. Age of onset is usually in the teens through early 20s, and patients often have a history of allergies, especially allergic rhinitis and/or asthma.
• Giant papillary conjunctivitis. A type of conjunctivitis associated with contact lenses. This type of conjunctivitis is believed to be an allergic reaction involving proteins that stick to the surfaces of contact lenses and other prosthetic devices or surgical sutures. As the name implies, bumps appear on the inner surface of the upper eyelids. This may also have non-allergy-related causes.

An untreated bout of seasonal or perennial allergic conjunctivitis rarely leads to long-term complications. However, the problem can spread to other parts of the eye and cause inflammation of the iris, or colored part of the eye. Vernal conjunctivitis and atopic keratoconjunctivitis have the potential to damage sight.

Allergic conjunctivitis is often confused with other forms of conjunctivitis, commonly known as “pink eye.” Pink eye refers to conjunctivitis caused by a viral infection. Allergic conjunctivitis occurs as the result of an allergic reaction. The eyes contain a large number of mast cells, which are a part of the immune system. An allergy is the body's inappropriate or exaggerated response to a substance it believes is harmful.

Conjunctivitis can also be caused by other factors, including:

• Bacterial infection (bacterial conjunctivitis)
• Chemical irritation
• Eye injuries
• Other forms of irritation that do not involve the immune system
• Parasites (rare)
• Fungal infection (rare)

Allergic conjunctivitis tends to occur more frequently in individuals who have other types of allergies, particularly allergic rhinitis. Unlike bacterial and viral conjunctivitis, allergic conjunctivitis is not contagious.

Conjunctivitis has many causes, all of which affect the clear lining that covers the white of the eye. Infection from bacteria or viruses causes bacterial and viral conjunctivitis, respectively.

Allergic conjunctivitis is a reaction to some type of allergen. When the eye comes into contact with a substance to which a person is allergic, histamine is released from mast cells within the eye, causing blood vessels in the membrane covering the eye to swell. A large percentage of those who suffer from allergic rhinitis also develop associated allergic conjunctivitis.

Common allergens that trigger allergic conjunctivitis include:

• Pollen. Small, powdery grains of flowering plants that can easily become airborne. These are most often produced by trees, grass and weeds.
  

  
  

• Dust. Mixture that contains tiny particles of soil, plant material, human and animal skin, hair, fabric fibers and insect parts.
  
  
• Dander. Small scales or flakes of dead skin cells that are continually shed by all animals.
  
  
• Molds and mildews. Tiny fungus spores that can become airborne. These often thrive outdoors in soil, vegetation and rotting wood. They can be found indoors as well, especially in damp areas, basements and bathrooms.

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• Eye drops/contact lens solutions. Preservatives in these formulas sometimes can make individuals more sensitive to an allergic reaction.
  
  
• Other irritants. Irritants known to trigger allergic conjunctivitis include tobacco smoke, chalk dust and perfume. Avoid these whenever possible.

While conjunctivitis that is not triggered by allergies often affects only one eye, allergic conjunctivitis usually affects both eyes at the same time. Allergic conjunctivitis also tends to affect both eyes equally, though one eye sometimes is afflicted more severely than the other.

The primary symptom of allergic conjunctivitis is itchy eyes. The surface of the eyeball also takes on a puffy appearance, though vision usually remains unimpaired. The conjunctiva (the mucous membrane covering the white of the eye and inside of the eyelids) reddens and there is a large amount of watery discharge. Allergic conjunctivitis sometimes spreads to the eyelids, which may become red, dry or scaly.

Signs and symptoms of allergic conjunctivitis will vary, but may include:

• Mild eyelid swelling
• Itching and burning
• Tearing of the eye
• Dilated vessels in the conjunctiva
• Watery or stringy mucus-like discharge
• Eye redness
• Sensitivity to light (photosensitivity)
• Occasional blurred vision
• Allergic shiners (darkening under the eyes)
• Bumps on the inside of the eyelids
• Sleep difficulties

Though allergic conjunctivitis can appear on its own, it usually is associated with allergic rhinitis. However, a person who has itchy eyes, tearing of the eye or other symptoms does not necessarily have allergic conjunctivitis.

Allergic conjunctivitis should not be confused with other forms of conjunctivitis. Conjunctivitis is most often the result of viruses, which is what physicians call “pink eye.” Conjunctivitis also can be caused by bacterial infections, chemicals, eye injuries and irritation due to contact-lens use.

In order to diagnose the specific cause of conjunctivitis, physicians will closely study the appearance of the eye and consider the patient’s symptoms. When the conjunctiva becomes irritated and bloodshot, it often produces a discharge. In bacterial conjunctivitis, the discharge is usually thick and creamy. In allergic or viral conjunctivitis, the discharge is usually clear. In addition, non-allergic forms of conjunctivitis often include sandy or gritty eyes (as opposed to itchy), dandruff and/or pimples.

Intense swelling and itchiness of the eyelid are hallmarks of allergic conjunctivitis. A history of allergies is also considered in the diagnosis.

Once a physician determines that the conjunctivitis is caused by an allergic reaction, the next step is to identify the specific allergen to which the patient is sensitive. There are two basic methods of determining the cause of the allergen:

• Skin testing. During skin testing, a doctor will scratch, prick or inject a specific allergen into a patient’s skin and wait for 10 to 20 minutes to see if there is a reaction. The development of a small, raised, reddish area generally indicates a positive reaction.
  
  
  
• Blood testing. Skin testing is not practical for those with certain skin conditions. In such cases, a blood test may be the best way to measure whether or not an individual is allergic to a certain substance (e.g., dog dander, grass pollen). In this process, an allergen is introduced and a patient’s blood is checked for an increase of the IgE antibody, which indicates a potential allergy. 

The physician may also collect scrapings, secretions or discharge from the eye and evaluate the sample for the presence of eosinophils (a type of white blood cell). This can help determine the specific type of allergic conjunctivitis. For instance, eosinophils are less likely to be found in a conjunctival scraping when vernal conjunctivitis is present than with atopic keratoconjunctivitis.

Treatment of allergic conjunctivitis focuses on avoiding the allergen known to trigger a reaction and relieving symptoms once a reaction occurs.

Symptom relief can take many forms, including cool compresses to ease eye itchiness or over-the-counter “artificial tears” solutions that lubricate the eyes and help force out allergens. However, most people with allergic conjunctivitis seek symptom-relieving medications, some of which are available over-the-counter. Always consult a healthcare professional before using any over-the-counter medication.

Medications used to relieve allergic conjunctivitis symptoms include:

• Nonsteroidal anti-inflammatory drugs (NSAIDs). Medications that reduce inflammation by blocking production of prostaglandins (chemicals that contribute to inflammation during allergic reactions).
• Antihistamine eye drops. Medications that block the effects of histamines (chemicals released during and allergic reaction). They can relieve the itching, burning and tearing associated with allergic conjunctivitis. However, they should not be used more than four times a day, and some healthcare professionals caution that these medications contain preservatives that may further aggravate symptoms. Oral antihistamines may also be recommended.
• Mast cell stabilizers. Medications that prevent mast cells from releasing histamines which trigger allergy symptoms.
• Low-dose corticosteroid eye drops. A type of anti-inflammatory medication similar to hormones found in the body. They can be used to treat allergic conjunctivitis, but only with caution and under a physician’s close monitoring. Long-term use can lead to the formation of cataracts, which are a clouding of the eye lens that can impact vision. The treatment can also cause glaucoma, which is increased pressure in the eye that can lead to blindness.

Allergy shots (immunotherapy) also may be used to desensitize the patient to the effects of the allergen that is causing symptoms. These shots contain a small amount of the allergen and are given on a regular schedule, such as once or twice a week for six months. If the individual shows no adverse reaction, the amount of allergen is increased with each successive injection. Over time, the body’s immune system learns not to react to the presence of the allergen. However, these injections are not always successful in treating the allergy.

Patients who wear contact lenses may also be advised to wear glasses until their symptoms subside.

It is not currently possible to prevent a person from developing an allergy. However, it is possible to prevent or reduce the frequency of allergic reactions that result from the allergy.

The most effective method of preventing an allergic reaction is to completely avoid the allergen known to trigger symptoms. There are many different triggers for allergic conjunctivitis, and patients should modify their behavior and surroundings based on which allergens provoke their allergic reactions.

Steps to avoid allergens that commonly trigger allergic conjunctivitis include:

• If pollen triggers the condition, try to stay indoors with the windows closed during periods when the pollen count is especially high (usually in the morning). Wearing eye goggles or breathing masks while mowing the lawn also can reduce exposure to pollens.
  
  
• Air conditioners and air filters can help prevent allergic conjunctivitis in those who are sensitive to dust particles. In addition, washing bedding often in at least 130 degree Fahrenheit (54 degrees Celsius) water, and using special allergen-proof covers for pillows, mattresses and box springs, can reduce exposure to dust mites.
  
  
• Avoiding close contact with animals can help those whose allergic conjunctivitis is triggered by animal dander. Cleaning a pet’s paws and fur before it enters the house can prevent allergens from getting inside.   
  
  
• Individuals who are sensitive to mold may benefit from limiting their exposure to damp areas (e.g., basements) and avoiding yard work such as mowing the lawn and raking leaves. Use of air conditioning and dehumidifiers can help prevent mold indoors. The use of humidifiers should be limited.

In addition, patients with allergic conjunctivitis may be advised to:

• Avoid wearing contact lenses or using contact lens solutions. These may make individuals more sensitive to an allergic reaction. Never share a contact lens with another person.
• Avoid wearing eye makeup. Some cosmetics contain allergens or irritants that can trigger an allergic reaction. Never share cosmetics with others.
• Avoid eye drops (unless recommended by a physician). Preservatives in these formulas sometimes can make individuals more sensitive to an allergic reaction.
• Wash their hands often with soap and water. Hands come into contact with the face often and can transfer allergens from surfaces to the eye area, triggering symptoms.
• Avoid touching their face or rubbing their eyes. These can further irritate the eyes and worsen symptoms.
• Avoid irritants, such as tobacco smoke, chalk dust and perfume. These may trigger or worsen eye-related symptoms.
• Consult a physician about whether or not allergy shots (immunotherapy) might be beneficial. This process can desensitize the patient’s body to the effects of allergens, thereby reducing the likelihood of developing allergic conjunctivitis.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctors the following questions regarding allergic conjunctivitis:

1. Do my symptoms indicate conjunctivitis that is allergy-related?
   
   
2. What methods will you use to determine if I have allergic conjunctivitis?
   
   
3. Would I benefit from allergy skin or blood testing?
   
   
4. What allergen is triggering my reaction?
   
   
5. What treatments are available to me? How effective are they?
   
   
6. When can I expect my symptoms to subside?
   
   
7. Am I a candidate for allergy shots?
   
   
8. Am I likely to develop allergic conjunctivitis again?
   
   
9. How can I lower my risk of having a reaction?
   
   
10. Can I continue to wear contact lenses?
    
    
11. Am I at any risk for potential complications? Is my vision in danger?