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.
^ McNeil DG. Topical Tenofovir, a Microbicide Effective against HIV, Inhibits Herpes Simplex Virus-2 Replication Archived 2017-04-09 at the Wayback Machine. NY Times. Research article: Andrei G; Lisco A; Vanpouille C; et al. (October 2011). "Topical Tenofovir, a Microbicide Effective against HIV, Inhibits Herpes Simplex Virus-2 Replication". Cell Host. 10 (4): 379–89. doi:10.1016/j.chom.2011.08.015. PMC 3201796. PMID 22018238.
"When you are having an outbreak of oral herpes, symptoms usually start with a burning, itching or tingling sensation on your lips," Michael says. "This will intensify until a small rash, and then blisters, appear. These sores are commonly called 'cold sores'. The blisters are usually filled with a clear or slightly yellow liquid. Over a short time, these blisters will burst leaving a painful, raw area. These will then dry and scab over. The scabs will generally fall off after a week or two, leaving fresh clear skin beneath."