How to know if your partner has herpes

It’s possible to get herpes from your partner. The likelihood of transmission depends on several factors, like if they have active sores, if they’re taking antiviral medication, and if you use condoms.

Many people ask their healthcare providers about how they can prevent spreading genital herpes to other people. Most people are surprised to hear that they can spread herpes simplex virus (HSV) even when they don’t have active symptoms. This is called “asymptomatic shedding.” And it means you can get HSV even if your partner doesn’t have actual sores on their genitals. Despite these risks, you can take action to prevent transmission.

Here are the main things to know about reducing the risk of transmitting HSV from someone with an infection to someone who doesn’t have one.

How is herpes transmitted?

Herpes simplex virus 2 (HSV-2) is the virus that most commonly causes genital herpes. It can spread through direct contact with herpes sores. But it can also spread even when no visible signs are present — through contact with skin or mucous membranes (like the mouth or vagina). And many infected people may not know they have herpes. In fact, estimates show that over 87% of people with an HSV-2 infection never get diagnosed. 

What are the chances of getting herpes from an infected partner?

This is a difficult question to answer. It depends on these factors: 

• The type of sex you have

• Whether active genital lesions are present

• Condom use

• The frequency of sex acts

• Whether the susceptible partner has a weakened immune system

• Whether the infected partner is taking antiviral therapy  

Most research on HSV transmission comes from studies on heterosexual couples. So more research is needed to know how transmission rates change or vary in same-sex or transgender couples.

HSV-2 transmission probability in heterosexual couples

The CDC estimates that over 775,000 people get new genital herpes infections every year. In heterosexual couples, men are less likely than women to get herpes from an infected partner. Condom use can lower that risk for women up to 96%. It’s somewhat less helpful in protecting susceptible men (65% reduced risk).

The likelihood of transmission seems to vary among studies, but many of the reports range between 3% and 10%. In one small study, the rate at which infected men transmitted herpes to women was 2.9 times per 100 unprotected sex acts. 

But, in a different study, almost 10% of female partners acquired herpes from a male partner over the course of a year. In yet another large study, published in the New England Journal of Medicine (NEJM), the risk of getting herpes from an infected partner was 3.6% over the course of 8 months. It’s unclear how many couples in this study used condoms.

Other than abstaining from sexual contact, there is no proven way to completely prevent getting infected by your partner. While condoms can help reduce the chance of transmission, they don’t completely eliminate the risk. However, another option to further reduce the risk of spread is daily antiviral medication. More on this next.

Can Valtrex prevent herpes transmission?

While there’s no cure for HSV-2, there are medications that can decrease the length and severity of outbreaks. And some people take daily valacyclovir (Valtrex) treatment to reduce asymptomatic shedding and the likelihood of transmission. 

In the same NEJM study, they also looked at how daily Valtrex affected transmission rates. Researchers divided the couples into two groups. In one group, the infected partner took daily Valtrex. In the other group, they took a placebo pill. Each group had over 700 couples. In the group that took daily Valtrex, only 14 people (1.9%) became infected with the virus — and only 4 of them developed an outbreak. In the group that took placebo, 27 people became infected. This showed that taking Valtrex 500 mg daily reduced the transmission of genital HSV-2 to the uninfected partner.

Although HSV-2 causes most recurrent genital herpes, an increasing number are caused by HSV-1 transmitted during oral sex. HSV-1 is the herpes simplex virus most commonly associated with cold sores on and around the mouth. Valtrex can be helpful to reduce transmission of HSV-2. But researchers have not studied it in people with genital lesions due to HSV-1. 

For people who have 9 or fewer recurrences of an HSV-2 outbreak per year, the dosage of Valtrex is typically 500 mg daily. For those who have more frequent outbreaks, kidney problems, or a weakened immune system, dosing may be adjusted. 

How long does it take for Valtrex to work?

It’s important to keep in mind that Valtrex is not a cure for genital herpes. And contagious lesions or shedding may still occur while taking the medication. Daily treatment can reduce the risk of transmission, but it isn’t 100% guaranteed that you won’t become infected.

If your partner has an active outbreak (lesions and/or other symptoms), it’s best to avoid sexual contact even if they’re taking the medication. It’s impossible to know if and when asymptomatic shedding is happening, so experts advise consistent condom use as an additional precaution.  

Can you have an outbreak while taking Valtrex?

Yes. Studies show that daily Valtrex reduces genital herpes outbreaks by 70% to 80%, but it’s still possible to have an outbreak while taking the medication. However, the frequency of outbreaks tends to go down over time for a lot of people. 

Is Valtrex better than Zovirax or Famvir?

Valtrex is not the only medication approved to treat genital herpes. To treat herpes outbreaks, valacyclovir (Valtrex), acyclovir (Zovirax), and famciclovir (Famvir) appear to be equally effective. Zovirax is only approved to treat initial and recurrent outbreaks. Compared to Famvir, Valtrex appears to be more effective at suppressing viral shedding when taken daily. Of the three medications, Valtrex is the only one approved for reducing the transmission of genital herpes.

Can you get herpes from oral sex?

Although it’s less common, you can get herpes from oral sex. Any contact with mucus membranes or skin with an infected partner has the potential to transmit herpes. Both HSV-1 (which causes cold sores) and HSV-2 can cause genital herpes. People with weakened immune systems can get herpes in the esophagus (the tube connecting the mouth to the stomach) from contact with HSV in the genital region.

The bottom line

Genital herpes (HSV) can be transmitted to uninfected partners even when an infected person does not have genital sores. Many people who carry HSV do not even know they’re infected. Herpes is very contagious and common, so it’s important to use condoms consistently and correctly. This can help reduce transmission if one partner has herpes. 

If a partner knows they have had HSV, taking a daily antiviral medication can reduce the chances of passing it along to partners. But neither condoms nor antiviral medications can completely eliminate the risk of transmitting herpes to other people. 

GoodRx Health has strict sourcing policies and relies on primary sources such as medical organizations, governmental agencies, academic institutions, and peer-reviewed scientific journals. Learn more about how we ensure our content is accurate, thorough, and unbiased by reading our editorial guidelines.

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