Acids with a pH of less than 2 or alkalis with a pH above 12 are capable of causing the most extensive injuries in ingestions. Alkalis damage tissue by saponifying fats, leading to liquefaction necrosis which allows the alkalis to reach deeper tissues. Acids denature proteins via coagulation necrosis, this type of necrosis is thought to prevent the acid from reaching deeper tissues. Clinically, the pH, concentration, volume of ingested substance in addition to the duration of time in contact with tissue as well as percentage of body surface area involved determine the severity of the injury.