The underlying cause of blepharitis has yet to be determined. Contributory factors include infection, genetics and hormones. The eyelid is frequently colonised by bacteria such as Staphylococcus epidemidis and Propionobacter acnes. In other patients, particularly those with asthma and eczema, the eyelids are colonized with Staphylococcus aureus.

When the meibomian gland secretion is examined under the microscope, we frequently see a louse-like creature named Demodex, which may also play a role in blepharitis. Hormones are important too. The meibomian glands exhibit oestrogen receptors and I have had patients whose symptoms have improved with drugs targeted at hormone receptors. (These drugs are quite powerful and used to treat some cancers and are not suitable or even licensed for blepharitis). Finally, we know that blepharitis is more common in some racial groups than others, for example it is more frequent in fair-skinned Northern Europeans.