The white part of your eye and the inner surfaces of your eyelids are covered by a transparent membrane (thin layer of cells) known as the conjunctiva. If the conjunctiva becomes inflamed, you have a condition called conjunctivitis. There are three types of conjunctivitis: irritant, allergic and infective. Each type of conjunctivitis is caused by different factors.
Infective conjunctivitis can be caused by a virus, bacteria or, in rare cases, by a sexually transmitted infection such as chlamydia or gonorrhoea. The most common symptoms include reddening and watering of the eyes. You may also notice a sticky coating on your eyelashes, particularly when you first wake in the morning, which can make your eyes feel like they're stuck together. Infective conjunctivitis is a very common condition and is responsible for 35% of all eye-related problems recorded in GP surgeries. It is most common in children and the elderly. Infective conjunctivitis rarely requires any medical treatment because the infection will normally heal by itself, usually within one or two weeks. For most people, the condition does not cause any complications. Those most at risk of developing complications from infective conjunctivitis are newborn babies, who are 28 days old or younger. An infection in the eye at a very young age can cause permanent damage. If you have infective conjunctivitis that is caused by a sexually transmitted infection (STI), your condition may last several months, rather than weeks.
Irritant conjunctivitis occurs when an irritant such as chlorine or an eyelash gets into your eyes. This can make your eyes sore and if you rub them it can irritate them more. Avoiding the irritant and not rubbing your eyes will help. However, if your eyes are very red and painful, you should seek medical help immediately.
Allergic conjunctivitis occurs when your eye comes into contact with an 'allergen'. An allergen is a particular substance that makes your body's immune system react abnormally, causing irritation and inflammation in the affected body part.