Version July 2025
| Bacterial | Viral | Allergic | |
| Epidemiology | Children | Adults | Young adults and adults |
| Seasonality | Fall, winter, early spring | Summer | Spring, may be recurrent |
| Systemic symptoms | May be associated with acute otitis media. | May be associated with viral prodrome, including adenopathy, fever, pharyngitis, or upper respiratory tract infection. There may be preauricular lymphadenopathy. | Nasal congestion, sneezing, wheezing. |
| Itching | Limited to none. | Limited to none. Primary complaint is grittiness, burning, or irritation. | Primary complaint. May also report grittiness, burning, or irritation. |
| Ocular discharge | Mucopurulent, and may be yellow, white, or green. May recur at lid margins and corners of the eye within minutes of wiping lids. Less commonly, watery discharge may also be seen. | Watery with strands of mucus. Less commonly, purulent discharge may also be seen. | Watery. |
| Conjunctival appearance | Pink or red. | Pink or red. Very rarely hemorrhagic. Tarsal conjunctiva may have a follicular or "bumpy" appearance. | Pink. Bulbar conjunctiva may be chemotic (puffy). Tarsal conjunctiva may have a follicular or "bumpy" appearance. |
