Large redness and swelling after a bug bite, if not accompanied by pain and fever, is generally due to an allergic reaction caused by the stimulation of subcutaneous tissue by the bug’s saliva or other secretions. At this time, you can use soap and water, glycolic lotion or local cold compress to reduce the skin temperature and reduce the symptoms of redness and swelling, and topical halometasone cream or mometasone furoate cream can be applied topically. Generally with the treatment of redness and swelling area gradually reduced, no need to be too nervous. Do not scratch vigorously to avoid scratching leading to lump breakage and increasing the risk of infection. If allergic reactions such as redness, swelling, itching and pain are evident after the bite, or if there is no improvement after the above treatment, antihistamines such as loratadine and cetirizine can be applied as prescribed by the doctor to relieve allergic symptoms. In addition, if there is a large area of redness and swelling accompanied by pain or fever, it may be combined with an infection, which requires active anti-infection treatment in the hospital, such as oral penicillin, erythromycin or azithromycin and other antibiotics, as well as topical creams, such as mupirocin ointment. If symptoms persist without relief or even worsen, treatment is required under the guidance of a doctor to avoid secondary infections caused by improper treatment, which can lead to serious consequences such as necrotizing fasciitis.