Redness of the Eye
Redness of the eye can be a sign of many conditions and diseases that our eyes may contract. The three major causes of red eye are dry eye, infections caused due to bacteria or virus, or allergies. There are at least a dozen different types of infections. Also, an allergy itself can be of various types like Seasonal Allergic Conjunctivitis, Urban Allergy, Perennial Allergic Conjunctivitis, Atopic Keratoconjunctivitis, Giant Papillary Conjunctivitis and many others.
What Causes Eye Allergies?
Just like hay fever and skin rashes, eye allergies develop when the body's immune system becomes sensitised and overreacts to something that is ordinarily harmless. An allergic reaction can occur whenever that "something" - called an allergen - comes into contact with your eyes. The allergen causes certain cells in the eye (called mast cells) to release histamine and other substances or chemicals that cause blood vessels in the eyes to swell, and the eyes to become itchy, red and watery.
What Allergens Trigger Eye Allergies?
Allergens that may be present indoors or outdoors can cause eye allergies. the most common outdoor airborne allergens are grass, tree and wood pollens. People who are sensitive to these allergens suffer from seasonal allergic conjunctivitis, the most common type of eye allergy. Pet hair or dander, dust mites and moulds are the most common indoor allergens. These indoor allergens can trigger symptoms for some people throughout the year, resulting in perennial allergic conjunctivitis.

Although cigarette smoke, perfume and diesel exhaust may inflame your eyes, they act as irritants rather than triggering an allergic response. They can, however, make your allergy symptoms worse.

It is important to diagnose the cause of redness correctly before deciding the course of treatment.

At the first sign of persistent redness or irritation in the eye, consult your eye specialist.
Do's & Dont's for Eye Allergy
Do's
1) If your eyes itch, wash them frequently with clean, cold water.

2) Place cold compress on your eyes.

3) Wear glasses instead of contact lenses to reduce irritation.

4) Wear goggles while taking a walk or gardening to reduce pollen expose.

5) When returning from outdoors, take a shower and change clothes right away.

6) Wash your hands before applying ointment or using eyedrops. 
Dont's
1) Don't rub your eyes.

2) Avoid wearing eye make-up on a regular basis.

3) Never share contact lenses or eye make-up with anyone.

4) Don't self medicate; consult your eye specialist as early as possible if allergy symptoms persist.