Conjunctivitis Caused by Irritation
Conjunctivitis may be caused by allergies or other irritants. This includes eyedrops, most of which contain preservatives that may cause eye irritation. The problem can keep coming back. Sometimes an eye infection will result. Treatment involves relieving the symptoms and avoiding the cause of the irritation. An infection, if present, will be treated.

Allergies
Grass, pollen, dust, mold, and animals are common causes of allergies. They make the eyes red, watery, and itchy. In most cases, both eyes are affected.
Treating the irritation. The best way to control an allergy is to avoid its source. Cold compresses and eyedrops can help reduce the swelling. They can also help relieve redness and itching. If your allergy is severe, your doctor may prescribe eyedrops or oral medications. Symptoms may take several weeks to clear up.
Other Irritants
Pollution, smoke, contact lenses, and makeup can irritate the eyes. The eyes get red, sore, puffy, and watery. One or both eyes may become irritated.
Treating the irritation. The best thing to do is avoid the irritant. Artificial tears can help flush out the eye and lubricate the surface. Your doctor may also prescribe eyedrops to reduce swelling and relieve redness. In certain cases, you may have to stop wearing contact lenses or eye makeup.