A method of measuring the stress or relaxation level of a mammal and a method of measuring the activity of the sympathetic nervous system of a mammal by measuring quantititative levels of deoxyhemoglobin and oxyhemoglobin are disclosed. Preferably, the levels of deoxyhemoglobin and hemoglobin are measured by a noninvasive technique, such as spectroscopy. A method of changing the activity of the sympathetic nervous system of a mammal is also disclosed, wherein the method includes a step of administering an effective amount of sensory regimen to the mammal. The method is useful for humans who are operating vehicles or machinery, who are suffering from cardiovascular disease or related complications, who are pregnant, or who are preparing for sleep. In addition, a method of improving the complexion of the skin of a mammal is disclosed.