Conjunctivitis, also known as pink eye, is the inflammation of the conjunctiva, which is the mucous membrane over the whites of the eyes as is also found on the inner side of the eyelids. In most cases the condition affects both eyes simultaneously, but there is the possibility that it can start in one eye and spread to the other after a couple of days. There's also the possibility that conjunctivitis is asymmetrical and will affect one eye more than the other. Conjunctivitis is a very common eye condition and it can be rather irritating and uncomfortable, but it is by no means serious. 

There are five different types of conjunctivitis, so therefore there are five unique causes of conjunctivitis. 

<b>Bacterial conjunctivitis</b>: This type of conjunctivitis is the result of bacteria such as staphylococci, streptococci or haemophilus. These kinds of organisms may be the result of the patient's own upper respiratory tract or skin, and they may even occur from another person with conjunctivitis. 

<b>Viral conjunctivitis</b>: In most cases viral conjunctivitis is associated with the common cold. It can be the result of a virus called 'adenovirus.' This type of conjunctivitis is highly contagious and can spread swiftly between several people and has the potential to cause a conjunctivitis epidemic. In most cases, viral conjunctivitis symptoms are paired with more of a watery discharge that is nether yellow nor green in color. This type of conjunctivitis is most prevalent in the early spring and late fall. Cold-like symptoms such as runny nose and sinus congestion may also occur, and in some cases the eyelids can become swollen and looking at intense light can be painful. 

<b>Chlamydial conjunctivitis</b>: This type of conjunctivitis is the result of an organism known as Chlamydia trachomatis. This organism can also spread and affect other parts of the body and has the potential to cause the sexually transmitted infection chlamydia.

<b>Allergic conjuctivitis</b>: Allergic conjunctivitis is very common in those who have other symptoms of allergic disease such as asthma, eczema and hay fever. This kind of conjunctivitis occurs from certain antigens such as dust mites, cosmetics or pollen. 

<b>Reactive conjunctivitis</b>: Reactive conjunctivitis is also known as chemical or irritant conjunctivitis. There are some people who are sensitive to particular chemicals in swimming pools or to fumes or smoke. This in turn can result in an irritation of the conjunctiva with watering, discomfort and redness. In these cases the irritants should be avoided in order to prevent another outbreak of conjunctivitis.