Adverse effects of glycerin are mainly due to its dehydrating effect. Oral administration of glycerin may cause headache, nausea, and vomiting; diarrhea. The incidence of adverse reactions such as thirst, dizziness, and confusion is low. Cardiac arrhythmias have also been reported. Glycerol increases plasma osmolality and leads to extravascular interstitial dehydration, resulting in extracellular fluid expansion, especially in cases of sudden dehydration, which can lead to circulatory overload, pulmonary edema, and heart failure. Therefore, glycerol must be used with caution in patients with excessive blood volume, heart failure or at risk of renal disease. Glycerin must also be used with caution in patients who are dehydrated, as severe dehydration may occur. After glycerol metabolism, diabetic patients may also develop hyperglycemia and glycosuria. Hyperglycemic hyperosmolar nonketotic coma is rare, but deaths have been reported. Intravenous administration of glycerol can cause hemolysis, hemoglobinuria, and acute renal failure. Local or rectal administration can produce some irritation. Prior to corneal application of glycerol, local anesthetics can be used to reduce the likelihood of painful reactions. Glycerin can keep the skin moist, but pure glycerin should not be applied directly to the skin to moisturize the skin, because if pure glycerin is applied directly to the skin, it will not only absorb the moisture in the air, but also suck out the water in the skin tissue, and as a result, the skin will be drier or even burned.