Inclusion Criteria:  • Participants who underwent open thyroidectomy between February 2019 and March 2021 at the Thyroid Cancer Center, Department of otorhinolaryngology, Seoul National University Bundang Hospital  Exclusion Criteria:  age younger than 20 years or older than 60 years history of keloid development requirement for modified radical neck dissection previous neck surgery current pregnancy or breast feeding allergy to PDRN taking medications that may affect inflammation and would healing such as isotretinoin, anti-cancer drugs, high dose corticosteroids, and anticoagulants uncontrolled medical diseases