Unilateral facial edema may be nephritis, but also heart disease, allergy, and dengue. 1. Nephritis: this disease is characterized by eyelid edema after waking up in the morning, and as the disease progresses, it can gradually lead to lower leg edema. In severe cases, the whole body can be edematous. 2. Heart disease: Severe heart disease patients can have generalized edema, and if they often lie on their side, they can have swelling on the side of their face. 3. Allergy: one side of the face after contact with allergens, such as unsuitable cosmetics, skin care products, etc., which may lead to the expansion of the skin capillaries on that side, congestion, edema, and ultimately lead to redness and swelling. 4. Dengue: Swelling on one side of the face may be a bacterial infection, which invades the surface layer of the skin, subcutaneous, lymphatic and other tissues, resulting in redness and swelling in the infected part of the face. One-sided facial swelling should be taken seriously, it is recommended to go to the hospital as soon as possible, follow the doctor’s instructions standardized treatment, so as not to delay the condition.