A recurrence is not as straightforward as "blistering genitals equals herpes episode." Blistering does mean a herpes episode, but that's not the only time it can spread.
Genital herpes is a virus and a sexually transmitted disease (see How Viruses Work to find out how viruses pass from person to person). It almost always spreads via sexual contact, through both skin-to-skin contact and through body fluids, like blood and semen. As with some other STDs, it spreads more easily from man to woman than from woman to man, because women typically experience more tearing of tissue during intercourse. During oral sex, any tear inside the mouth can lead to contraction. HSV-1 can also spread via oral sex or kissing, and both virus types can spread from one part of the body to another -- if you have a cut on your finger and you touch an open genital sore, you can end up with a herpes sore on your finger.
Herpes, when it's first contracted, occurs in three stages. The primary stage is the most obvious: That's when people usually notice something is wrong, what with all the blisters and open sores and sometimes fever, flulike symptoms, and painful or difficult urination, among other unpleasantness. The disease can spread during this stage.
In the second, "latent" phase, there are no symptoms. This is when the virus is travelling through the body, heading for your spinal nerves. The virus doesn't spread during the latent phase.
The final phase of initial infection is, for conscientious people who would never knowingly spread the disease, the most problematic. In the "shedding" stage, there are no symptoms, but the virus can spread.
To further complicate matters, some people who contract herpes never experience any noticeable symptoms at all. They may be totally unaware they're carrying the virus, but they can still spread it to their partners.
And to further, further complicate matters, even in people who do experience noticeable symptoms in their disease, herpes can spread during a flare-up when there are not yet any visible sores. The virus can still be present in the skin. This happens during a "flare-up," or recurrence, which can happen sporadically for years after the initial infection. Recurrences manifest as milder versions of the primary-infection stage, typically only with sores, fewer than during initial infection.
Given the likelihood of spreading herpes when there are no cold sores or no noticeable cold sores, keeping the virus to yourself while remaining sexually active may seem like a lost cause. But there are some precautions you can take to reduce the likelihood of passing herpes to your partner.