Lower eyelid suddenly swollen, may be staying up all night, but also may be infectious factors, or local allergies, mosquito bites and so on. 1. Staying up late: Staying up late and not getting enough sleep may lead to sudden swelling of the lower eyelids. 2. Infectious factors: bacterial infection caused by conjunctivitis, or local skin folliculitis, skin soft tissue infections, can also lead to sudden swelling of the lower eyelids. 3. Localized allergies: allergic reactions caused by the use of cosmetics and skin care products or topical medications can also lead to sudden swelling of the lower eyelids. 4. Mosquito bites: mosquito bites on the skin of the lower eyelid can also cause sudden swelling of the lower eyelid. Lower eyelid suddenly swollen, there may be other reasons, it is recommended to go to the hospital in time to check, clear cause.