How Allergies cause Eye Redness?

When your eyes are exposed to allergy-causing substances,

• a substance called histamine is released by your body.
• The blood vessels in the conjunctiva become swollen.
• The eyes can become red, itchy, and teary very quickly.

Symptom:

The pollens that cause symptoms vary from person to person and from area to area.

Treatment:

Antihistamine eyedrops: These can reduce 

1. itching,
2. redness,
3. swelling associated with eye allergies.

Although these drops provide quick relief, the effect may last only a few hours, and some must be used four times a day.