Blepharitis is inflammation of the eyelids. It usually involves the eyelid margins where the eyelashes grow and affects both eyelids. It's a common cause of sore, red eyelids and crusty eyelashes.
The openings (orifices) of oil glands located near the eyelashes become occluded. The pursuing changes lead to irritated and red eyes. Blepharitis is usually associated with an overgrowth of bacteria along the eyelid margins forming a structure called “biofilm”. And, parasitic eyelash mites called “Demodex” feed on this film. Consequently, the overgrowth of these mites on “biofilm” causes a worsening of the eyelid inflammation.