| Bacteria | Most common:
  - Staphylococci
 - Streptococci
 - Moraxella
 - Haemophilus
  Rare:
  - Pseudomonas (in contact lense users may lead to corneal perforation)
 - Chlamydia, gonococci, Francisella tularensis
  
 | 
| Viruses | Adenoviruses the most common; others: Herpes simplex 1 and 2, H. varicella-zoster, EBV | 
| Fungi | Candida albicans the most common (associated primarily with immunodeficiency or long-term use of topical glucocorticoids) | 
| Parasites | Itch mites, pubic lice (in eyelashes), lice (in eyebrows); in tropical countries loiasis, onchocerciasis , among others | 
| Allergy | Pollen, food substances, eye drops in long-term use | 
| Dry eye syndrome Dry Eye Syndrome | Often caused by an underlying eyelid dysfunction. Predisposing factors may also include systemic diseases or pharmaceuticals. |