Blepharitis is where the edges of your eyelids become red, swollen and irritable. According to the National Eye Institute, Blepharitis is caused by an imbalance of bacterial on your eyelids at the base of your eyelashes.  Granted, having bacteria on your skin is 100% normal and everyone does, the issue is predominantly caused by a build-up of unwanted bacteria. It can, however, also be caused by clogged or irritated oil glands within the eyelid itself.