Eyelid swelling in hot weather may be caused by drinking too much water before going to bed, improper diet, mosquito bites, allergic blepharitis and other reasons. 1. Drinking too much water before going to bed: Due to the hot weather, if patients drink a lot of water before going to bed, the body’s function to expel water decreases, resulting in water retention around the eyes, which manifests itself as eyelid swelling. 2. Improper diet: when the weather is hot, if the patient often eat barbecue, long-term high salt and spicy will lead to the body’s toxins can not be successfully discharged from the body, resulting in eyelid swelling. 3. Mosquito bites: swollen eyelids in hot weather may also be caused by mosquito bites, patients may find red spots or hard nodules on the eyelids, accompanied by itching. 4. Allergic blepharitis: swollen eyelids in hot weather can also be caused by allergic blepharitis, when the weather is hot, there will be a large number of pollen, dust mites and other allergens suspended in the air, when the skin of the eyes and allergens come into contact with the skin, will lead to swelling of the eyes, redness, itching and other symptoms. Eyelid swelling may also have nothing to do with the hot weather, it is recommended that patients with long-term eyelid swelling, immediately go to the hospital to avoid delaying the condition and causing adverse consequences.