One swollen eye and one not swollen may be caused by other reasons such as allergic conjunctivitis, blepharocyst, blepharitis, and orbital cellulitis. 1. Allergic conjunctivitis: Allergic conjunctivitis is mainly caused by contact with allergens, and the patient will have eyelid swelling, photophobia, tearing, eye itching, redness of the white eyeballs, burning eyes and other manifestations. If a patient has allergic conjunctivitis in one eye, it will show that one eye is swollen and the other is not swollen. 2. Blepharophalangeal cysts: Blepharophalangeal cysts are caused by blepharitis, chronic conjunctivitis and other diseases that lead to the blockage of the secretion port of the blepharophalangeal gland. The patient will manifest as eyelid lumps, foreign body sensation in the eyes, blurred vision and other manifestations. Therefore, patients with blepharocysts in one eye will have the symptom that one eye is swollen and the other is not. 3. Blepharitis: Blepharitis is mostly considered to be caused by staphylococcal infection, and patients will have localized redness, swelling, heat and pain, hard nodules and other manifestations. If the patient has blepharitis in one eye, one eye is swollen and the other is not. 4. Others: Swelling in one eye may be caused by orbital cellulitis, eyelid trauma, and eyelid boils. It is recommended that patients who have a swollen eye need to consult a doctor in a timely manner, and need to follow the doctor’s instructions to choose the appropriate method of treatment.