It should not be confused with conditions caused by other viruses in the herpesviridae family such as herpes zoster, which is caused by varicella zoster virus. The differential diagnosis includes hand, foot and mouth disease due to similar lesions on the skin. Lymphangioma circumscriptum and dermatitis herpetiformis may also have a similar appearance.
Herpes virus type 1 (HSV-1) is the cause of cold sores or fever blisters around the mouth. Usually, the sores or blisters can show up on the outside of the mouth or on the lips. But sometimes, they can be inside the mouth, on the face, nose, cheeks or fingers. HSV-1 can also lead to infection of the genitals, called genital herpes. This occurs when you have a cold sore and perform oral sex on another person. HSV-1 infections are highly contagious. Apart from oral-genital contact, they can be spread through skin-to-skin contact. If you come into contact with a person or a thing that carries HSV-1, you will be likely to get it, too. Often, people get HSV-1 from kissing someone with a cold sore or when they share eating utensils, razors, or towels.
OK, so the majority of people have it. Just this year, the World Health Organization released a study that estimates two thirds of people in the world (67%) have the HSV-1 strain of the herpes simplex virus — that’s approximately 3.7 billion people worldwide. While HSV-1 typically refers to oral herpes infections, it also includes some genital infections. The new report estimates that half of the HSV-1 infections in people between the ages of 15–49 are actually genital infections transmitted via oral-to-genital contact. The Center For Disease Control (CDC) estimates that 1 in 6 people have genital herpes.
^ 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.
Herpes of the mouth is a viral infection. The virus HSV-1 may be transmitted by droplet spread – direct contact with saliva or even respiratory droplets. These droplets must make contact with broken skin or the mucous membranes in order to infect a person. The method of spread can involve kissing an infected person or even through touch. It can also be spread through the use of contaminated kitchen utensils. Sexual contact accounts for a small number of cases of HSV-1. Nevertheless it is a consideration when genital lesions are present. HSV-2 on the other hand is usually transmitted through sexual contact.
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.