There are many reasons for left-sided facial edema, physiologically, normal people sleep on the left side for a long time, affecting lymphatic reflux, which may lead to left-sided facial edema, pathologically, such as facial soft tissue infections, trauma, allergies, mosquito bites and so on will appear on the left side of the face edema. 1. Physiology: in normal people sleeping on the left side for a long time, affecting lymphatic drainage, may lead to left-sided facial edema, improve the sleeping position, generally can be relieved on their own. 2. Pathology: Pathologically, soft tissue infections (such as cellulitis, dengue, mumps, etc.), allergies, trauma, mosquito bites, left facial neuropathy (such as trigeminal neuritis, etc.), and left facial tumors on the left side of the face may cause left-sided forehead edema. If the swelling on the left side of the face is serious, or if the symptoms persist and do not improve, the patient should go to the hospital in time for treatment.