Itchy, painful, red and swollen eyes are mostly caused by eye diseases, such as blepharitis, allergic conjunctivitis and keratitis. 1. Blepharitis: Blepharitis is an acute purulent inflammation of the eyelid glands, mostly caused by staphylococcal infections, and patients often have acute inflammatory manifestations such as redness, swelling, itching and pain in the eyes. 2. Allergic conjunctivitis: Allergic conjunctivitis is an inflammation caused by hypersensitivity of eye tissues to allergens, and common allergens include willow flakes, dust particles, animal fur, mites and so on. When the conjunctiva comes into contact with these allergens, an allergic reaction occurs, resulting in symptoms such as itching, redness, swelling and pain. 3. Keratitis: Keratitis is an inflammation caused by external or endogenous pathogenic factors attacking the corneal tissue, which can lead to eye pain, redness, swelling, itching, photophobia, tearing and other symptoms. Itchy, painful, red and swollen eyes can also be caused by other reasons, and should be promptly consulted by a doctor for targeted treatment.