Conjunctivitis is an extremely common condition that affects adults, children and babies. It usually affects one eye first then after a short while affects both eyes.
Bacterial and viral conjunctivitis are very contagious and can spread easily from person to person.
Bacteria that can cause conjunctivitis include:
- Staphylococcus spp
- Streptococcus pneumoniae
- Haemophilus influenzae
- Moraxella catarrhalis
- Neisseria gonorrhoeae
- Chlamydia trachomatis
Viral conjunctivitis is commonly due to an adenovirus infection, which can also cause fever and a sore throat. Some types of adenovirus can cause keratitis, a more serious condition where the cornea of your eye becomes inflamed.
Viruses that can cause conjunctivitis include:
- Herpes simplex
- Herpes zoster
- Molloscum contagiosum (poxvirus)
Sometimes parasites such as lice can infect the eyelashes causing conjunctivitis. People on immunosuppressant therapy after an organ transplant, or to treat cancer or AIDS, are more likely to get viral conjunctivitis.
Allergic conjunctivitis isn’t contagious but is an response to allergens in the environment such as:
- Pollen
- Dust mites
- Animal hair
- Chemicals
- Cosmetics
If you have hay fever or there’s a family history of allergies you may be more susceptible to allergic conjunctivitis.