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.

Jamie*, 29, is HSV-positive and contracted herpes from her husband. But, she explains, “He only had one outbreak when he was young and that was it. So he didn't realize what it was.” Jamie was infected three years into their relationship simply because he had outbreaks that infrequently. She says, “I was worried he had cheated on me, but then found similar stories online, and our outbreak patterns underscore that what happened is very possible.”
Avoid physical contact with anyone who has visible blisters and sores, and don't share towels or anything that may have come into contact with the sores. "It is also important that before you have any intimate contact with anyone you ask them about their sexual health, whether they have a herpes infection or have ever had any other sexually transmitted infection," Michael advises. "This is because statistically, people who have had an STI are more likely to be infected with the herpes virus. Using condoms and dental dams can also help reduce your risk of catching oral herpes."
Traditionally, it was assumed that HSV-1 strictly caused oral sores and blisters, whereas HSV-2 caused genital and/or rectal sores and blisters. However, the virus- or perhaps just our understanding of the virus itself- has evolved in such a way that doctors now recognize that either HSV-1 or HSV-2 can cause genital and/or rectal sores, albeit with HSV-2 causing the majority of sores in the genital or rectal areas.
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.
During these periods, it is especially important to abstain from kissing and any form of physical contact with the blistering area, saliva, or sexual discharge. If you are infected, be sure to wash your hands after touching an infected area on either the oral or genital regions. Herpes medications can also help reduce your risk of transmitting the virus to another individual.
As with almost all sexually transmitted infections, women are more susceptible to acquiring genital HSV-2 than men.[41] On an annual basis, without the use of antivirals or condoms, the transmission risk of HSV-2 from infected male to female is about 8–11%.[37][42] This is believed to be due to the increased exposure of mucosal tissue to potential infection sites. Transmission risk from infected female to male is around 4–5% annually.[42] Suppressive antiviral therapy reduces these risks by 50%.[43] Antivirals also help prevent the development of symptomatic HSV in infection scenarios, meaning the infected partner will be seropositive but symptom-free by about 50%. Condom use also reduces the transmission risk significantly.[44][45] Condom use is much more effective at preventing male-to-female transmission than vice versa.[44] Previous HSV-1 infection may reduce the risk for acquisition of HSV-2 infection among women by a factor of three, although the one study that states this has a small sample size of 14 transmissions out of 214 couples.[46]

Genital herpes is contracted through sexual activity, and may show symptoms around the genital area (anus, buttocks, thigh, penis, vulva, etc.). Additionally, people with HIV can experience significantly worse symptoms of herpes.  See a doctor if your partner has herpes, or if you notice any unusual sores on your body.  How do you know if you have herpes?  Read more in our Diagnosing Herpes section here.  
Pain, sore lips, burning sensation, tingling, or itching occurs at the infection site before the sores appear. These are the early symptoms (prodrome). Sometimes these symptoms happen prior to the appearance of sores, bumps, pimple-like lesions, or blisters (herpes or herpetic stomatitis). Thereafter, clusters or groups of painful blisters (also termed fever blisters) or vesicles erupt or ooze with a clear to yellowish fluid that may develop into a yellowish crust. These blisters break down rapidly and appear as tiny, shallow gray ulcers on a red base. Fever blisters are smaller than canker sores. A few days later, they become crusted or scabbed and appear drier and more yellow.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
"Oral herpes is an infection found in the mouth, or on and around the lips, caused by the Herpes Simplex Virus (HSV)," Michael explains. "There are two types or strains of this virus called HSV1 and HSV2. Usually, the HSV1 strain infects the mouth and lips, and the HSV2 strain infects the genitals. It is however possible for HSV2 to infect your mouth and lips."
×