How long does an outbreak last?

The first outbreak

A first, or primary, episode is the longest and most uncomfortable one most people will have. It can involve tender blisters or sores, and many people also feel generally unwell for a few days, rather as though they were fighting off flu.

UK guidance treats the first five days as the window that matters. The NHS advises that antiviral medicine is prescribed for a first infection to stop symptoms getting worse, and that it should be started within five days of symptoms appearing. The BASHH national guideline puts it slightly differently and more usefully: treatment should be given within five days of the start of the episode, while new lesions are still forming. Patients are typically reviewed at day five, and treatment may be continued to seven to ten days if new lesions are still appearing.

So the honest range for a first episode is a couple of weeks rather than a couple of days, and the guidance is built around catching it early rather than waiting to see how bad it gets.

Later recurrences

After the first episode, later outbreaks are called recurrences, and they are a different proposition: shorter, milder, and usually without the feeling of being unwell all over. Many people learn to spot a prodrome — tingling, itching or a warning ache a day or two before anything appears.

How often they come varies enormously. The median rate after a symptomatic first episode is 0.34 recurrences a month — roughly four a year — for HSV-2. For HSV-1 in the genital area it is about four times less frequent. And the same guideline notes that recurrence rates decline over time in most people, though it is careful to say the pattern is variable.

That is worth holding onto if you have just been diagnosed: the frequency you are dealing with in the first year is not usually the frequency you will be dealing with in five. More on the pattern in outbreaks and triggers.

Cold sores

An oral cold sore is the same family of virus in a different place. The NHS says cold sores usually clear up on their own within 10 days. That is the clearest single timeframe in any of the guidance, which is partly why cold sores feel so much less frightening than the identical virus a few inches lower. We wrote about that double standard in cold sores.

What treatment actually changes

This is where honest numbers matter, because the gap between what people hope and what the evidence shows is wide.

For a recurrence, the BASHH guideline is blunt: antivirals reduce the duration and severity, and the reduction in duration is a median of one to two days. The NHS says much the same — an antiviral may shorten an outbreak by a day or two if you start it as soon as symptoms appear.

The other approach is daily suppression, which is a different goal: not shortening a single outbreak, but reducing how often they happen at all, and lowering the risk of passing it on. That is covered in suppression and transmission.

Why timing matters more than dose

Across the guidance, one theme repeats: what determines whether treatment helps is when you start it, not how much you take. Antivirals work on virus that is actively replicating, which is why the guidance keeps pointing at the window while new lesions are still forming.

The practical consequence is that a course kept at home, ready to start at the first prodrome, is worth considerably more than the same course collected three days into an outbreak. That is the entire logic of a rescue pack.

When to get seen

Get seen sooner rather than later if this is a first episode — the treatment window is short, and a diagnosis needs a swab taken while sores are present. A sexual health clinic is the right place: many offer walk-in appointments and often get test results back faster than GP practices, and you do not need a referral.

Seek help urgently if you cannot pass urine, if the pain is severe, if you feel seriously unwell, or if you are pregnant and think you may be having a first episode — see herpes and pregnancy.