Why would a third-degree burn be less painful than a first- or second-degree burn involving the same body area?

A third-degree burn would be less painful than a first- or second-degree burn involving the same body area because of the destruction of underlying pain receptors.
Nerve endings are destroyed in third-degree burns, which means that a person can no longer feel pain in that particular spot on the body. Third-degree burns are the most severe ones and cannot be treated easily - usually skin grafting or synthetic skin has to be used to replace the burnt skin.