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What causes blepharitis?
Blepharitis involves the eyelid margins, where the eyelashes grow and the openings of the tiny oil glands are located. There may be involvement of the skin adjacent to the outer edges of the eyelid margins and/or the inner edge of the eyelid that comes into contact with the eyeball secondary to the underlying disorder of the lid margins.
Most cases of blepharitis are posterior blepharitis, due to inflammation of the meibomian glands of the lids. There are about 40 of these glands in each of the upper and lower lids. The openings of each gland lie behind the eyelashes. The eyelid margins can become inflamed, irritated, and itchy when these glands produce abnormal secretions. Blepharitis is often seen in patients with acne rosacea, a common disorder of the oil glands of the skin of the face.
Anterior blepharitis is due to inflammation of the lid margin around the lashes. Seborrheic blepharitis is similar to dandruff of the scalp.
Allergies due to reactions from mascara, contact lens solutions, sprays, exposure to animals, environmental chemicals, or airborne allergens can also cause blepharitis.
Less commonly, inflammation of the lids can be caused by a primary infection of the eye lids by bacteria such as Staphylococci or infestation of the lashes by tiny mites (Demodex) or head lice.