Pink eye is also known as conjunctivitis. This is an infection or inflammation of conjunctiva (the transparent membrane) which lines your eyelid and covers the white part of the eyeball. It is known that when small blood vessels in the conjunctiva become inflamed, then they are more visible. This is a reason what is causing the whites of your eyes to appear pink or reddish. The pink eye is very commonly caused by viral or bacterial infection or an allergic reaction. In babies the pink eye can be caused by incompletely opened tear duct . This condition can be irritating but there are rare cases when it is affecting your vision. There are many treatments which can ease the discomfort that is caused by pink eye. This condition can be contagious so this is a reason why it needs early diagnosis and treatment of pink eye can help to limit its spread.
Pink eye symptoms
Here are the most common symptoms of pink eye:
- There can be a discharge in one eye or in both eyes that forms a crust during the night that may prevent your eyes or eyes from opening in the morning 
- A gritty feeling in one or both eyes
- Itchiness in one or both eyes
- Redness in one or both eyes
It is known that there are serious eye conditions which can cause eye redness. They can cause light sensitivity, a feeling that something is stuck in your eye (foreign body sensation) and eye pain, then you should visit your doctor as soon as possible. 
Pink eye Causes
Here are the most common causes for pink eye:
- In newborns, a blocked tear duct 
- A foreign object in the eye 
- A chemical splash in the eye
Types of pink eye: Here are given the three types of pink eye:
- Viral and bacterial conjunctivitis: It is known that most cases of pink eye are caused by a virus. These types of conjunctivitis can happen along with colds or symptoms of respiratory infection, such as a sore throat. Also if you wear contact lenses which are not your own or you wear contact lenses which are not cleaned properly, then it can cause bacterial conjunctivitis. Both types of conjunctivitis are very contagious. These types of conjunctivitis spread through direct or indirect contact with the liquid which drains from the eye of some person who is infected. One eye or both eyes can be affected by bacterial or viral conjunctivitis. 
- Allergic conjunctivitis: This type of conjunctivitis is affecting the both eyes. It is a response to an allergy – causing substance such as pollen. Your body is producing an antibody called IgE (immunoglobulin) which is in response to allergens. The IgE is triggering special cells that are known as mast cells which are in the mucous lining of the eyes and airways to release inflammatory substances in which histamines are also included. It is known that the release of histamine by your body can produce many allergy signs and symptoms in which pink or red eyes are also included. Those people who have allergic conjunctivitis can experience inflammation, tearing and intense itching of their eyes, as well as watery nasal discharge and sneezing. Allergy eye drops are controlling most of the allergic conjunctivitis. [3,6]
- Conjunctivitis resulting from irritation: When there is irritation from a foreign object or a chemical splash in the eye, then it can lead to conjunctivitis. Also there are some cases when the flushing and cleaning of the eye to rid of that object or chemical can cause irritation and redness. The signs and symptoms of this type of conjunctivitis, such as a mucous discharge and watery eyes, usually clear up on their own in a period of about a day.
Risk factors: Here are some factors which are increasing the risk of pink eye:
- Using contact lenses, especially extended – wear lenses 
- Exposure to someone infected with the viral or bacterial form of conjunctivitis 
- Exposure to something for which you have an allergy (allergic conjunctivitis) 
Complications: The pink eye can cause inflammation in the cornea which is affecting the vision. This can happen in both children and adults. The prompt evaluation and treatment are needed by your doctor because they can help to reduce the risk of complications.
 Mallika PS, Asok T, Faisal HA, et al. Neonatal conjunctivitis – a review. Malaysian Family Physician. 2008;3(2):77–81.
 Boyd K. What is sleep crust? American Academy of Ophthalmology. Retrieved from www.aao.org/eye-health/diseases/what-is-sleep-crust
 Azari AA, Barney NP. Conjunctivitis: A systematic review of diagnosis and treatment. JAMA. 2013;310(16):1721–9.
 Farokhfar A, Amiri AA, Mohammad AHG, Sheikhrezaee M. Common causes of red eye presenting in northern Iran. Romanian Journal of Ophthalmology. 2016;60(2):71–8.
 Yeu E, Hauswirth S. A review of the differential diagnosis of acute infectious conjunctivitis: Implications for treatment and management. Clinical Ophthalmology. 2020;14:805-13.
 La Rosa M, Lionetti E, Reibaldi M, et al. Allergic conjunctivitis: a comprehensive review of the literature. Italian Journal of Pediatrics. 2013;39:18.
 Donshik PC. The effect of contact lenses on the conjunctiva. Advances in Corneal Research. 1997;451-7.