Hello, Thank you for your question and welcome to Health Care Magic. I read your query and I understand your concerns. The description you are making, makes me suspect of jaundice, also referred to as icterus, which is the yellow staining of the skin and sclerae (the whites of the eyes) by abnormally high blood levels of the bile pigment, bilirubin. Except the yellowish color and weight loss, does your son have any signs or symptoms, in order to make me easier helping you? The lifestyle of your son makes me suspect of hepatitis, which could be type A due to the ingestion of infected food, hepatitis B or C if your son has had unprotected sex or injected drugs. With such a presentation on my clinic, I would perform at least liver function tests, complete blood count (CBC), electrolyte panel, lipase levels, and urinalysis. Blood testing for exposure to hepatitis may also be ordered. Additional blood testing may be ordered based on the initial results. Depending on the results of initial blood tests, further studies may be needed to help diagnose the underlying disease process. Hope I helped with my answer. For further concerns or follow up questions feel free to ask again. Kind Regards, Dr. Ina