Single eyelids suddenly become double eyelids may be due to: more fat in the upper eyelid, lack of sleep, or false double eyelids, pathologic double eyelids and so on. The details are as follows: 1. More fat in the upper eyelid, due to sleep or vigorous blinking, will form a fault and become double eyelids. With the sagging of upper eyelid fat, it will become single eyelid again. 2. False double eyelids: the blepharoplasty line is shallow, babies and children have a slightly higher water content, and the subcutaneous tissues of the eyelids are lax and more prone to edema. Therefore, it looks like a single eyelid. Double eyelids will appear after puberty is fully developed. 3. Pathological double eyelids: If a single eye suddenly becomes double eyelids, accompanied by eyelid edema, redness or itching, it may be caused by inflammation and allergy. Please go to the regular hospital for diagnosis and treatment in time, do not delay the condition. If the single eyelid becomes double eyelids and is accompanied by other eye discomforts such as redness, swelling and itching, it is recommended to consult a doctor as soon as possible and follow the doctor’s instructions.