Canker sores are sometimes thought to be caused by HSV, but this is not true. Canker sores occur only inside the mouth, on the tongue, and on the soft palate (roof of mouth), not on skin surfaces. Although they reoccur, they are not contagious, usually are self-limiting, and have almost no complications. Canker sores are caused by substances that irritate the lining of the mouth.
Herpes simplex is a viral infection caused by the herpes simplex virus.[1] Infections are categorized based on the part of the body infected. Oral herpes involves the face or mouth. It may result in small blisters in groups often called cold sores or fever blisters or may just cause a sore throat.[2][5] Genital herpes, often simply known as herpes, may have minimal symptoms or form blisters that break open and result in small ulcers.[1] These typically heal over two to four weeks.[1] Tingling or shooting pains may occur before the blisters appear.[1] Herpes cycles between periods of active disease followed by periods without symptoms.[1] The first episode is often more severe and may be associated with fever, muscle pains, swollen lymph nodes and headaches.[1] Over time, episodes of active disease decrease in frequency and severity.[1] Other disorders caused by herpes simplex include: herpetic whitlow when it involves the fingers,[6] herpes of the eye,[7] herpes infection of the brain,[8] and neonatal herpes when it affects a newborn, among others.[9]
With the first outbreak of herpes virus infection, an individual may also experience nonspecific flu-like symptoms like fever, swollen lymph nodes, headache, and muscle aches. It is also possible to have herpes virus infection without having any symptoms or signs, or having signs and symptoms that are so mild that the infection is mistaken for another condition.

A doctor will base a presumptive diagnosis on information provided by the patient and on the physical examination. The characteristic appearance of the herpes sores leaves little doubt about the diagnosis, so the typical appearance of the sores is key to the diagnosis. This appearance helps distinguish oral herpes from oral thrush, shingles, gonorrhea, and syphilis. In addition, chapped or sunburned lips can resemble oral herpes, but the tissue stain (Tzanck smear, see below) shows no virus-induced cell changes. Further testing is usually not necessary but is sometimes done.
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