Conjunctivitis is also known as pink eye. It is called pink eye because it causes the whites of the eyes to go pink. Pink eye is the inflammation of the thin, clear covering (conjunctiva) of the white of the eye and inside of the eyelid. It is a very common eye issue, and is generally easy to treat.
The cause of conjunctivitis is based on what initially caused the eye infection.
There is viral conjunctivitis, which is caused by a virus (like the cold). This form of pink eye is very contagious, but clears up on its own fairly quick and does not require medical treatment.
There is Bacterial conjunctivitis, which is caused by bacteria entering the eye. It can be dangerous to your eyes health if left untreated.
There is Allergic conjunctivitis, which is caused by irritants like dust, or pollen. This can be seasonal (those who suffer from pollen allergies) or be on a flare up basis (by those who are allergic to dust or pet dander).
The symptoms of pink eye are roughly the same, but each form does have its own set of symptoms. All forms have an eye that is pink in appearance (hence the name).
With viral conjunctivitis the eyes become watery, itchy and are sensitive to light. This is highly contagious and can be spread by coughing or sneezing.
With bacterial conjunctivitis there is a sticky, yellow or greenish discharge that comes out of the corner of the eyes. This discharge can cause the eyelids to stick together. This is only contagious if there is a direct contact with the infected eye; there is a high chance that both eyes will be infected due to their close proximity and the chance of touching the infected eye with your hands.
With allergic conjunctivitis the eye are red, watery, burning and itchy. Both eyes are affected, but this is not contagious to others around.
Treatment for each form of conjunctivitis differs because you have to treat the underlining issue.
Viral conjunctivitis is generally left to run its course (in about one to two weeks), as antibiotics do not work on viruses (and the illness is generally mild enough that antivirals are not needed).
Bad cases of bacterial conjunctivitis will be treated with antibiotics, though most cases will again be left to run their course.
Allergic conjunctivitis can only be addressed by correcting the root cause. However, you can manage symptoms via medicated eye drops or antihistamines.