The 3 main types of conjunctivitis are bacterial, allergic and viral . Bacterial and viral conjunctivitis are both infectious types of conjunctivitis that can spread easily.
Bacterial conjunctivitis
This is caused by a bacterial infection and is common in infants and children. Typical symptoms include a sticky yellow or green ‘gunk’ or discharge, most noticeable as a crust on the eyelids on waking up. It's highly contagious (easily passed on to someone else).
Allergic conjunctivitis
Conjunctivitis caused by allergies can be seasonal, occurring at certain times of the year (if due to pollen or grasses), or continuous or ongoing (if caused by allergens such as dust mite or pets). Allergic conjunctivitis is not contagious. Read more about allergic conjunctivitis.
Viral conjunctivitis
This is often caused by the same virus that causes the common cold and other respiratory infections, eg, measles and the flu. It usually begins in one eye, then spreads to the other eye shortly after. It tends to cause redness, sensitivity to light and a thin watery or white mucous discharge. Viral conjunctivitis is very contagious.
Other causes
Inflammation of the conjunctiva can also be caused by direct contact with irritant chemicals in cosmetics, chlorine from swimming pools or preservatives (even some in eye drops). People who wear contact lenses can get eye irritation due to the lens or contact lens solutions and are also more likely to get eye infections.