Allergies is the most common and probably the most complex cause for red eye symptoms. In general allergies are poorly understood, for example we can not fully explain or cure many allergy induced disorders such as asthma, rosacea or chronic urticaria.

We can be allergic to almost anything, for example some researchers believe Rosacea is caused by an allergy to microscopic mite (Demodex folliculorum) that lives in the hair follicle. Knowing that eyes also provide a broad surface area for the collection of any airborne allergens it would not be surprising that some hidden allergy may be responsible for the adverse reaction, as people may experience allergic reactions limited solely to ocular tissues.

Perennial allergic conjunctivitis may last throughout the year and although itching is the key symptom for diagnosing ocular allergy disorders it is often absent in allergic conjunctivitis. Some types of allergies, for example hay fever, make the eyes itchy, while others may merely produce a chronic redness. It's not only invisible microscopic particles that are all around us and abnormal immune system that may cause red eye symptoms, hidden food allergies may also create an allergic reaction of the eyes with usual symptoms such as itchy or red eyes.

The first line treatment is identifying allergens and avoiding them. Common medicines used in ocular allergy treatment can be found at Review of Ocular Anti Allergy Products page. The most popular medicines used in ocular allergy are artificial tear drops (such as systane, theratears or refresh endura) and Patanol which is a combination of anti histamine and mast cell stabiliser. People who do not respond well to first line treatment may be prescribed with Alrex, which is a corticosteroid approved by FDA for the treatment of allergic conjunctivitis. Long term use of corticosteroids have serious side effects such as elevated eye pressure or a possible development of cataract, therefore some specialists use Restasis (cyclosporin) for long term anti inflammatory effect, especially when dry eye symptoms are observed. A new possible trend in allergic eye inflammation treatment may be anti - immunoglobulin E medicine (such as Xolair), which is currently only approved for asthma.