Hi, Sores in the mouth and on the palms of the hands and soles of the feet can be a symptom of several different conditions. The two conditions that you mentioned, herpes and erythema multiforme, are possibilities, but other conditions can also cause these symptoms. Herpes simplex virus (HSV) can cause sores in the mouth, as well as on the hands and feet. It is a contagious virus that can be transmitted through close contact with someone who has an active outbreak of the virus. Antiviral medications like acyclovir can help to manage symptoms of herpes, but they do not cure the virus. Erythema multiforme is a type of hypersensitivity reaction that can be triggered by certain medications, infections, or other factors. It causes red, raised lesions that may blister and can appear on the hands, feet, or other parts of the body. Treatment depends on the cause of the condition and may include corticosteroids or other medications to manage symptoms. Other conditions that can cause sores in the mouth and on the hands and feet include hand, foot, and mouth disease (caused by the coxsackievirus), Stevens-Johnson syndrome (a severe and potentially life-threatening reaction to medication), and pemphigus vulgaris (an autoimmune disorder that causes blisters on the skin and mucous membranes). Given that your son has been experiencing these symptoms for several years and has received different diagnoses, it may be helpful to seek a second opinion from another healthcare provider. They may recommend further testing or referral to a specialist in dermatology or infectious diseases. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician