Most modern dry cure hams also use nitrites (either sodium nitrite or potassium nitrate), which are added along with the salt. Nitrates are used because they prevent bacterial growth and, in a reaction with the meat's myoglobin, give the product a desirable dark red color. The amount and mixture of salt and nitrites used have an effect on the shrinkage of the meat. Because of the toxicity of nitrite (the lethal dose of nitrite for humans is about 22 mg per kg body weight), some areas specify a maximum allowable content of nitrite in the final product. Under certain conditions, especially during cooking, nitrites in meat can react with degradation products of amino acids, forming nitrosamines, which are known carcinogens.