Herpes spreads through direct skin-to-skin contact with an infected person, most often during kissing, oral sex, or genital sex. The virus can pass to you even when your partner has no visible sores, which is why herpes is so common: over 846 million people aged 15 to 49 are living with genital herpes infections worldwide, more than 1 in 5 adults.
There are two types. HSV-1 traditionally causes oral herpes (cold sores), while HSV-2 is the primary cause of genital herpes. But these categories blur in practice. HSV-1 increasingly causes genital infections through oral sex, and both types spread the same way: through contact with infected skin or mucous membranes.
Why Herpes Spreads Without Symptoms
The reason herpes spreads so effectively is a process called viral shedding. After your first infection, the virus travels along nerve fibers and settles permanently in nerve clusters near the spine. It stays dormant there most of the time. Periodically, small quantities of virus travel back down those nerve fibers to the skin surface, where they can be passed to another person through contact. This happens in short, repeated bursts from different spots, often without causing any sore or symptom you’d notice.
A large study published in JAMA measured how often people shed the virus on days with no symptoms. People who knew they had genital HSV-2 shed the virus on about 13% of days without any visible outbreak. People who had HSV-2 but had never experienced noticeable symptoms still shed the virus on roughly 9% of days. That means someone who doesn’t know they carry herpes can still transmit it on nearly one out of every eleven days.
Among those with recognized symptoms, the virus was detectable on about 20% of all days, including both outbreak days and silent shedding days. This is why most new herpes infections come from partners who either don’t know they’re infected or aren’t having an active outbreak at the time.
Oral Sex and HSV-1 Genital Infections
A growing share of new genital herpes cases are caused by HSV-1 rather than HSV-2. The route is straightforward: if your partner has oral herpes (even without a visible cold sore), they can transmit HSV-1 to your genitals during oral sex. The reverse is also possible. You can get genital herpes from receiving oral sex from someone with oral herpes.
This matters because HSV-1 oral infections are extremely common, often acquired in childhood from family members through casual kissing. Many people carry oral HSV-1 without ever connecting it to the possibility of genital transmission.
How Condoms Affect Transmission Risk
Condoms reduce herpes transmission, but their effectiveness depends on the direction of spread. One study found that condom use reduced the per-act risk of HSV-2 transmission from men to women by 96%. In the other direction, from women to men, condoms reduced per-act risk by about 65%, though that estimate was less statistically precise.
The difference comes down to anatomy. Condoms cover the primary source of viral shedding in men but can’t cover all potentially shedding skin in women. Areas like the upper thighs, buttocks, and skin around the genitals that aren’t covered by a condom can still shed the virus. Condoms are clearly protective, but they don’t eliminate the risk entirely.
Transmission During Pregnancy and Birth
Herpes can pass from mother to baby during vaginal delivery, and the risk varies enormously depending on when the mother was first infected. If a mother acquires a brand-new herpes infection around the time of delivery, the transmission rate to the baby is 50% or higher. This is because her body hasn’t yet built up antibodies that help suppress the virus and that cross the placenta to partially protect the baby.
For new infections that aren’t the mother’s first exposure to a herpes type (for instance, she already has HSV-1 and catches HSV-2), the transmission rate drops to around 30%. The lowest risk, less than 2%, occurs when the mother had herpes before becoming pregnant. In that scenario, her immune system has had time to develop antibodies that limit viral activity and offer the baby some protection during delivery.
Can You Catch Herpes From Objects?
Herpes is fragile outside the body, but it doesn’t die instantly. Research testing virus survival from active cold sores found that herpes can remain viable for up to two hours on skin, three hours on cloth, and four hours on plastic surfaces. In practice, though, transmission from objects like towels, razors, or cups is considered rare compared to direct person-to-person contact. The virus needs a moist environment and a way into the body, such as a small break in the skin or a mucous membrane. Sharing a drink is unlikely to transmit herpes, but sharing a razor with someone who has an active outbreak carries more theoretical risk.
Does Having One Type Protect Against the Other?
If you already carry HSV-1, it offers partial protection against HSV-2. Animal studies confirm that prior HSV-1 infection significantly reduces the severity of HSV-2 genital disease, with far fewer lesions developing compared to animals with no prior herpes exposure. However, this cross-protection is incomplete. You can still acquire HSV-2 if you already have HSV-1, and the WHO estimates that about 50 million people carry both types simultaneously.
The partial protection likely comes from shared immune responses. The two viruses are closely related, so the antibodies and immune cells your body builds against one type offer some recognition of the other. This tends to make a new HSV-2 infection milder and harder to notice, which can actually delay diagnosis.
What Reduces the Chance of Spreading It
Several factors lower transmission risk, and combining them is most effective:
- Avoiding contact during outbreaks. Viral shedding is highest when sores are present. Skipping sexual contact from the first tingling sensation through complete healing of any sores removes the highest-risk days.
- Consistent condom use. Even between outbreaks, condoms significantly reduce per-act transmission risk, especially from men to women.
- Daily antiviral medication. People who take suppressive antiviral therapy shed the virus on fewer days. Those who have never had noticeable symptoms shed about 50% less than those with recognized outbreaks.
- Disclosure and testing. Since most transmission happens from people who don’t know they’re infected, blood tests that detect herpes antibodies can clarify your status even without symptoms.
Herpes is most contagious in the first year after infection, when outbreaks tend to be more frequent and viral shedding rates are highest. Over time, the immune system suppresses the virus more effectively, and both outbreaks and shedding episodes typically decrease in frequency.