Many types of allergic and nonallergic conditions can trigger eye-related symptoms. Allergens that commonly cause eye-related symptoms include:

• Pollens
• Molds
• Dust
• Pet dander
• Latex

An allergic condition known as allergic conjunctivitis directly affects the eyes. It affects up to 22 percent of the U.S. population, according to the American College of Allergy, Asthma and Immunology (ACAAI). Allergic conjunctivitis manifests in three major forms:

• 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.
  

  

• 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 Down feathers.
  
  
• Vernal conjunctivitis. A chronic form of allergic conjunctivitis that occurs most often in the spring and fall. It has the potential to permanently damage vision and is more likely to occur in boys than in girls.

Itchiness is the symptom most often associated with allergic conjunctivitis, according to the ACAAI. Other symptoms include redness, tearing, burning and blurred vision.

An overall allergic reaction is likely to also trigger symptoms not related to the eyes. These include:

• Runny nose
• Nasal congestion

Nonallergic factors that can produce eye–related symptoms include:

• Viral conjunctivitis. Known as “pink eye,” it is caused by a virus.
  
  
• Bacterial conjunctivitis. Also known as “pink eye,” it is caused by bacterial infection.
  
  
• Blepharitis. Inflammation of the eyelids that can cause symptoms in the eyes and lids.
  
  
• Corneal ulcers. Usually caused by a bacterial, fungal, amoebic or viral infection that affects the clear front window (cornea) of the eye.
  
  
• Keratoconjunctivitis sicca. Reduced tear production sometimes known as “dry eye.” Most often afflicts seniors, but can occur at any age.
  
  
• Uveitis. Inflammation of the uvea, which includes the iris, ciliary body (the set of muscles that focuses the lens of the eye and produces the fluid in the eye) and choroid (the outer lining of the back of the eye).
  
  
• Airborne irritants, including tobacco smoke and smog.
  
  
• Chemical irritants, including cosmetics and pool chlorine.
  
  
• Obstruction of tear duct. A blockage in the tear passage that runs from the eyes to the nasal cavity. Most often afflicts babies.
  
  
• Foreign objects in the eye.
  
  
• Aged lids entropion (lids turning in) and ectropion (lids turning out).

Many people with allergies experience eye-related symptoms during flare-ups. Allergies affect the eyes because the mucous membrane covering the white part of the eye and the inner eyelid (conjunctiva) contains mast cells. During an allergic reaction, an allergen triggers a mast cell to burst, releasing histamine and other chemicals that cause symptoms. The result for the eyes is swelling, inflammation, burning and itchiness.

Symptoms such as watery eyes, itchiness, burning and redness are common for those with allergic rhinitis, latex allergies, food allergies and many other types of allergy conditions.