Conjunctivitis, commonly known as pink eye, is an inflammation of the conjunctiva—the clear membrane covering the white part of the eye and the inner eyelids. This inflammation causes small blood vessels to dilate, giving the eye its characteristic pink or reddish appearance. The time it takes for pink eye to become noticeable depends entirely on the underlying cause: viral infection, bacterial infection, or allergic reaction. Determining the specific cause is important because the timeline for symptom onset, duration, and contagiousness varies significantly.
The Incubation Period
The time between exposure to an infectious agent and the first appearance of symptoms differs for the two primary infectious causes. Viral conjunctivitis, often caused by adenoviruses responsible for the common cold, typically has an incubation period ranging from one to three days after initial contact. Symptoms of this contagious form often peak around day three to five of the illness.
Bacterial conjunctivitis, caused by various bacteria like Staphylococcus or Streptococcus, generally has a faster onset. Symptoms can appear within 24 to 72 hours of exposure, sometimes sooner, as the bacteria quickly colonize the eye’s surface tissues. Allergic conjunctivitis is not an infection and does not have a true incubation period. Instead, symptoms manifest immediately or within minutes to a few hours after the eyes encounter an allergen like pollen or pet dander.
Recognizing the Initial Signs
The moment pink eye “shows up” is marked by the earliest physical manifestations. Initial signs generally involve a feeling of grit or irritation, as if a foreign body were lodged in the eye, accompanied by noticeable redness. This irritation often leads to increased tearing, which may initially be the only symptom.
The type of discharge produced is often the key to distinguishing between the infectious causes. Viral pink eye typically presents with a watery, thin discharge and often begins in one eye before spreading to the other a few days later. This onset may also coincide with symptoms of an upper respiratory infection, such as a sore throat or runny nose.
Bacterial pink eye usually produces a thicker, pus-like discharge that is yellow, white, or greenish in color. This sticky material frequently causes the eyelids to crust over and stick together, particularly upon waking.
How Long Contagion Lasts
Once symptoms appear, the duration of contagiousness is key for preventing spread. For viral pink eye, a person is generally contagious as long as they are experiencing active symptoms, which can last for one to two weeks, and sometimes up to three weeks. Viral shedding, the release of infectious particles, can begin even before redness and discharge are fully apparent. Guidelines for returning to school or work often require waiting until tearing and redness have significantly improved or resolved.
Bacterial conjunctivitis remains contagious as long as ocular discharge is present. This period is much shorter if treatment is administered. Once antibiotic eye drops or ointment are started, the bacterial form typically ceases to be contagious after about 24 hours. Without antibiotic treatment, the infection may remain transmissible for approximately a week. Allergic conjunctivitis poses no risk of transmission to other people.