a method for distinguishing between a full thickness and a partial thickness skin burn in a patient having a skin burn . the methods includes administering a fluorescent compound , which is excited by infrared light , to the patient to cause the compound to enter one or more capillaries below and adjacent the skin burn . the compound is then excited with infrared light , and the amount of fluorescence of the compound caused by the infrared light detected at the skin burn and at unburned skin adjacent the skin burn . the ratio of fluorescence detected at the skin burn and at the unburned skin is an indication of the thickness of the skin burn , e . g ., a ratio of less than 0 . 4 indicates a full thickness skin burn .