Herpes is caused by the herpes simplex virus (HSV), which spreads through direct contact with infected skin, saliva, or genital fluids. There are two types: HSV-1, which typically causes oral herpes (cold sores), and HSV-2, which primarily causes genital herpes. Globally, around 846 million people between ages 15 and 49 have a genital herpes infection, and roughly 42 million new genital infections occur each year.
Two Viruses, Different Routes
HSV-1 spreads mainly through oral contact: kissing, sharing drinks, or any skin-to-skin contact involving the mouth area. It’s the virus behind most cold sores. However, HSV-1 can also cause genital herpes when transmitted through oral sex. HSV-2 spreads through sexual contact with genital or anal skin, sores, or fluids. You can carry both types at the same time, and an estimated 50 million people worldwide do.
The distinction matters less than people think. Either virus can infect either location. What differs is how often each type reactivates depending on where it lives. HSV-1 tends to cause fewer recurring outbreaks when it infects the genitals, while HSV-2 in the genital area reactivates more frequently.
How the Virus Gets In
HSV needs contact with mucous membranes (the moist tissue lining the mouth, genitals, or anus) or tiny breaks in the skin to establish infection. Once it enters, it travels along nerve fibers to clusters of nerve cells near the spine called sensory ganglia, where it sets up a permanent, dormant residence. This is why herpes is a lifelong infection: the virus hides in nerve tissue where the immune system can’t fully eliminate it.
The initial infection can show up as painful blisters or sores within a few days of exposure, though the timeline varies widely. Some people develop symptoms quickly, while others don’t notice anything at all during their first infection and only realize they carry the virus much later, if ever.
Spread Without Visible Symptoms
One of the most important things to understand about herpes is that it frequently spreads when no sores are visible. The virus periodically reactivates and reaches the skin surface without causing noticeable symptoms, a process called asymptomatic shedding. In the first year after infection, HSV-2 can be detected on the skin on roughly 26% of days. That rate drops over time, falling to about 13% of days between years one and nine, and around 9% of days after a decade.
This shedding is why most new herpes infections come from partners who don’t know they’re infected or aren’t experiencing an active outbreak. About 70% of neonatal herpes cases, for instance, result from exposure to a mother’s asymptomatic viral shedding near delivery.
What Triggers Outbreaks to Return
The virus itself is the cause of herpes, but several factors can wake it from dormancy and trigger a recurrence. UV light is one of the most well-documented triggers. In a controlled study, UV-B exposure induced herpes recurrences in over a third of unprotected treatment sessions, with sores appearing an average of about five days after exposure, typically at the exact skin site that received the UV light. This neural pattern confirms that the virus reactivates from its hiding place in nerve tissue and travels back down to the skin.
Other common reactivation triggers include:
- Physical or emotional stress, which can suppress immune function enough to let the virus reactivate
- Illness or fever, which is why cold sores are sometimes called “fever blisters”
- Hormonal changes, particularly around menstruation
- Skin trauma or friction in the affected area
- Fatigue and sleep deprivation
Not everyone experiences the same triggers, and some people have frequent recurrences while others go years between outbreaks.
Can You Get Herpes From Objects?
The risk is low but not zero. HSV-1 can survive on contaminated surfaces, but the amount of viable virus drops significantly within two hours and approaches zero by 24 hours. Different surface materials affect how long the virus lasts. The practical takeaway: sharing items like toothbrushes or personal devices with someone who has active oral or genital sores shortly before you use them carries some risk, but casual contact with doorknobs or toilet seats is not a realistic transmission route.
Transmission During Pregnancy
A mother can pass herpes to her baby, most commonly during delivery. About 85% to 90% of neonatal herpes infections happen during birth, with another 5% to 10% acquired shortly after. Only about 5% result from infection in the womb.
The timing of the mother’s infection makes a dramatic difference in risk. A new herpes infection acquired in the last trimester carries a 30% to 50% chance of neonatal transmission. A first infection earlier in pregnancy drops the risk to about 1%. For mothers with a history of recurrent herpes who aren’t having an active outbreak at delivery, the risk is extremely low, around 0.02% to 0.05%. This is because their immune system has already built antibodies that provide some protection to the baby.
How Much Condoms Reduce Risk
Condoms provide significant but incomplete protection. A study of couples where one partner had HSV-2 found that condom use reduced per-act transmission risk from men to women by 96%. Protection in the other direction, from women to men, was lower at about 65%, likely because herpes sores and viral shedding can occur on skin that a condom doesn’t cover. Since herpes spreads through skin-to-skin contact rather than through fluids alone, barrier methods help most when they cover the area where the virus is active.
Testing and Diagnosis
If you suspect herpes, the testing method matters enormously. DNA-based testing (PCR) of an active sore is the most accurate approach. Blood tests that look for antibodies are far less reliable. One study found that the accuracy of HSV-2 antibody testing was only about 38% for detecting HSV-2 alone, and combined antibody testing had an overall accuracy of roughly 35%. Early in infection, the body may not have produced detectable antibodies yet, leading to false negatives. And cross-reactivity between HSV-1 and HSV-2 antibodies can produce misleading results.
If you have a visible sore, getting it swabbed for PCR testing while it’s still active gives the clearest answer about which virus type is involved and whether herpes is actually the cause of your symptoms.