Herpes spreads through direct skin-to-skin contact with someone who carries the virus, whether or not they have visible sores at the time. There are two types: HSV-1, which typically causes oral herpes (cold sores), and HSV-2, which typically causes genital herpes. Both can infect either location, and both spread even when the infected person looks and feels completely fine.
The Two Types and How Each Spreads
HSV-1 transmits mainly through contact with sores, saliva, or skin surfaces in and around the mouth. Kissing is the most common route, but sharing drinks or utensils during an active outbreak can also do it. Less commonly, HSV-1 travels to the genitals through oral sex. Among people with a first-time genital HSV-1 infection, 50 to 100% reported receiving oral sex in the weeks before their outbreak.
HSV-2 spreads during vaginal, anal, or oral sex through contact with genital or anal skin, sores, or fluids. It can transmit even when the skin looks completely normal, and in fact it often does. HSV-2 is rarely spread through casual, non-sexual contact.
Why It Spreads Without Symptoms
This is the part that surprises most people. The virus periodically “sheds” from the skin surface with no sores, no tingling, and no warning. A large study tracking people with HSV-2 found that the virus was detectable on roughly 12% of days when no genital lesions were present. Even among people who had never noticed any symptoms at all, shedding occurred on about 9% of days.
More striking: among people who did get noticeable outbreaks, about 57% of their total shedding days were still subclinical, meaning the virus was active on the skin while they felt perfectly fine. For people with no recognized symptoms, that number jumped to 84%. The majority of herpes transmission happens during these invisible shedding episodes, which is why so many people are genuinely unaware they passed it on.
Oral Sex and Genital HSV-1
Roughly 10 to 15% of first-time genital herpes cases are caused by HSV-1 rather than HSV-2. The route is almost always oral sex. Someone with a history of cold sores (or who carries HSV-1 without knowing it) can transmit the virus to a partner’s genitals during oral contact. This can happen even without a visible cold sore, since HSV-1 also sheds from the mouth asymptomatically.
Genital HSV-1 tends to recur less frequently than genital HSV-2, but the initial outbreak can be just as painful. Many people don’t realize cold sores and genital herpes can be caused by the same virus, which makes oral-to-genital transmission an underappreciated risk.
What Doesn’t Spread It
Herpes requires direct contact with skin or mucous membranes. While the virus can technically survive on dry surfaces for anywhere from a few hours to several weeks under laboratory conditions (longer in low-humidity environments), real-world transmission from toilet seats, towels, or doorknobs is not considered a meaningful risk. The virus needs warm, moist conditions and a point of entry like a mucous membrane or a break in the skin. Casual contact like hugging, handshakes, or sitting next to someone does not transmit herpes.
How Long Before Symptoms Appear
If you do develop symptoms after exposure, they typically show up within 1 to 12 days for most people. Some cases take longer. In one clinical study, incubation periods ranged from 1 to 49 days in men and 1 to 28 days in women, with a handful of patients experiencing even longer delays. Many people never develop noticeable symptoms at all, which means they may carry the virus for months or years before an outbreak (if one ever comes) clues them in.
If you want to get tested after a possible exposure, blood tests that look for antibodies need time to become accurate. The CDC notes it can take up to 16 weeks or more after exposure for current blood tests to reliably detect infection. Testing too early can produce a false negative.
How Condoms Reduce the Risk
Condoms provide real but incomplete protection. A study of couples where one partner had HSV-2 found that condom use reduced per-act transmission risk by 96% from men to women and by about 65% from women to men. The difference comes down to anatomy: condoms cover the primary shedding site on the penis more completely than they cover all potentially exposed skin on the vulva and surrounding area.
Because herpes can shed from skin that a condom doesn’t cover (the thighs, buttocks, or areas around the genitals), condoms lower the odds significantly but don’t eliminate them entirely. Daily antiviral medication taken by the infected partner further reduces transmission risk and is often used in combination with condoms in couples where one person is positive and the other isn’t.
Transmission During Pregnancy
The risk of passing herpes to a baby during delivery depends heavily on timing. If a pregnant person contracts herpes for the first time near the end of pregnancy, the transmission risk to the newborn during vaginal delivery is 50% or higher. That’s because the body hasn’t yet built up antibodies that help protect the baby.
A new but non-primary infection (meaning the person already had one type of HSV and caught the other) carries a transmission rate around 30%. The lowest risk, less than 2%, occurs when the infection was acquired well before pregnancy, giving the immune system time to develop protective antibodies that cross the placenta. This is why providers screen for herpes history during pregnancy and may recommend antiviral medication or a cesarean delivery if an active outbreak is present at the time of labor.
Factors That Increase Your Risk
Several things make transmission more likely. Having sex with a partner during an active outbreak (visible sores, tingling, or prodromal symptoms) carries the highest per-act risk. Having multiple sexual partners increases the cumulative odds of encountering someone who is shedding the virus. Other sexually transmitted infections, particularly those that cause genital sores or inflammation, can compromise the skin barrier and make it easier for herpes to enter.
Friction during sex can create microscopic breaks in the skin that give the virus a foothold. The mucous membranes of the genitals, anus, and mouth are thinner and more permeable than regular skin, which is why these are the primary sites of infection. People with weakened immune systems may shed the virus more frequently and are also more susceptible to acquiring it.