The most common reason that people develop cold sores on their mouths is due to becoming infected with HSV-1. (4) HSV-1 usually causes cold sore breakouts around the lips or mouth, or what some people describe as “fever blisters.” Someone can become infected with HSV-1 starting as a child, and then the virus can lay dormant in the body until the immune system is weakened, at which point symptoms can surface.
In infants for whom the condition is quickly diagnosed and controlled by antiviral medication, prognosis is good. However, in untreated and undiagnosed infants, the virus can attack the body’s organs systems, causing serious and potentially life-threatening complications, including seizures and Encephalitis, which can cause brain and/or spinal damage.
In all cases, HSV is never removed from the body by the immune system. Following a primary infection, the virus enters the nerves at the site of primary infection, migrates to the cell body of the neuron, and becomes latent in the ganglion.[14] As a result of primary infection, the body produces antibodies to the particular type of HSV involved, preventing a subsequent infection of that type at a different site. In HSV-1-infected individuals, seroconversion after an oral infection prevents additional HSV-1 infections such as whitlow, genital herpes, and herpes of the eye. Prior HSV-1 seroconversion seems to reduce the symptoms of a later HSV-2 infection, although HSV-2 can still be contracted.

^ 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.
There are two types of herpes simplex virus, type 1 (HSV-1) and type 2 (HSV-2).[1] HSV-1 more commonly causes infections around the mouth while HSV-2 more commonly causes genital infections.[2] They are transmitted by direct contact with body fluids or lesions of an infected individual.[1] Transmission may still occur when symptoms are not present.[1] Genital herpes is classified as a sexually transmitted infection.[1] It may be spread to an infant during childbirth.[1] After infection, the viruses are transported along sensory nerves to the nerve cell bodies, where they reside lifelong.[2] Causes of recurrence may include: decreased immune function, stress, and sunlight exposure.[2][3] Oral and genital herpes is usually diagnosed based on the presenting symptoms.[2] The diagnosis may be confirmed by viral culture or detecting herpes DNA in fluid from blisters.[1] Testing the blood for antibodies against the virus can confirm a previous infection but will be negative in new infections.[1]
If not treated immediately, it has potential  spread to other parts of the body. Being highly contagious in nature it gets readily transmitted by sharing utensils, clothes, and toothbrush. Maintaining sexual contact, kissing and touching also leads to the spread of virus. It is likely to spread more when the virus is present with physical outbursts. It is less contagious if the virus is present without any outward physical signs.
Although the cause is unknown, outbreaks are often associated with periods of weakened immune systems, skin wounds, menstruation, fever, nerve damage, tissue damage from surgery, or exposure to extreme climate situations. A genital herpes outbreak or episode occurs when the HSV-1 or HSV-2 virus is reactivated from its dormant stage. Genital herpes is an incurable disease, and once you contract it, you may experience outbreaks throughout your lifetime. Those who are experiencing their first herpes episode of genital herpes can expect to have several (typically four or five) outbreaks within a year. Over time these recurrences usually decrease in frequency and severity. The first outbreak of herpes is often the longest outbreak experienced. After that, short and inconsistent episodes can be managed and treated with antiviral medication.
Herpes is transmitted via skin-to-skin contact, not through blood or saliva. Cullins explains that someone with HSV can be shedding the herpes virus without having an outbreak (known as asymptomatic virus shedding), and infect somebody that way. Suppressive antiviral medications, like acyclovir or valacyclovir, inhibit HSV replication, which decreases shedding but does not completely eliminate it, says Johnston.
There’s herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). “HSV-1 and HSV-2 are different but closely related viruses,” says Dr. Christine Johnston, MPH, who is the Associate Medical Director of the Virology Research Clinic at the University of Washington. Johnston explains that both are transmitted through close mucosal or skin contact with infected secretions. HSV-1 primarily causes oral outbreaks, also known as cold sores, and HSV-2 usually causes genital outbreaks. But HSV-1 can also cause genital outbreaks through oral-to-genital contact, according to the CDC. According to Johnston, genital HSV-1 is less likely to recur than HSV-2, and there’s less asymptomatic shedding (transmitting the virus without realizing it) with HSV-1 than with HSV-2.
Once a person is infected, there are no symptoms for anywhere between 2 days to 2 weeks. This is known as the incubation period and is the time during which the virus multiplies profusely. The first symptoms that are seen are the small fluid-filled blisters known as vesicles. This arises as the virus starts destroying cells at the site and causes intense localized inflammation. These small vesicles or sometimes the larger bullae may either burst resulting in ulcer or heal completely with no scarring. The virus may also travel from the site of infection and “hides” by the sensory dorsal root. Here it remains latent until is it is reactivated.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
The “classic” symptoms that most people associate with genital herpes are sores, vesicles, or ulcers – all of which can also be called “lesions.” (The scientific literature on herpes uses the term “lesion” to describe any break or irregularity in the skin.) These classic lesions of genital herpes often resemble small pimples or blisters that eventually crust over and finally scab like a small cut. These lesions may take anywhere from two to four weeks to heal fully.
The risk of transmission from mother to baby is highest if the mother becomes infected around the time of delivery (30% to 60%),[54][55] since insufficient time will have occurred for the generation and transfer of protective maternal antibodies before the birth of the child. In contrast, the risk falls to 3% if the infection is recurrent,[56] and is 1–3% if the woman is seropositive for both HSV-1 and HSV-2,[56][57] and is less than 1% if no lesions are visible.[56] Women seropositive for only one type of HSV are only half as likely to transmit HSV as infected seronegative mothers. To prevent neonatal infections, seronegative women are recommended to avoid unprotected oral-genital contact with an HSV-1-seropositive partner and conventional sex with a partner having a genital infection during the last trimester of pregnancy. Mothers infected with HSV are advised to avoid procedures that would cause trauma to the infant during birth (e.g. fetal scalp electrodes, forceps, and vacuum extractors) and, should lesions be present, to elect caesarean section to reduce exposure of the child to infected secretions in the birth canal.[14] The use of antiviral treatments, such as aciclovir, given from the 36th week of pregnancy, limits HSV recurrence and shedding during childbirth, thereby reducing the need for caesarean section.[14]
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.
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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