How herpes is tested for

The definitive test is a swab of an active lesion, sent for laboratory analysis. A small sample of fluid is taken from the affected area with something like a cotton bud. It is quick, and it can usually identify whether herpes simplex is present and which type it is.

The catch is the window. The test depends on there being virus present to find, so it works best early in an outbreak, while blisters are fresh or newly opened. Once things have crusted and started healing, the chance of a clear result drops.

Which produces the single most useful piece of practical advice on this page: if you have something now, get seen now. Do not wait for it to settle down before booking. The instinct to wait until it looks less alarming is entirely understandable and it is the thing that most often costs people an answer.

Blood tests look for antibodies — your immune system's response — rather than the virus itself. That makes them useful in a narrow set of circumstances and misleading in others, which is why they are used carefully rather than routinely.

• They cannot tell you where. Antibodies show exposure to the virus, not which part of the body it settled in. A positive HSV-1 result cannot distinguish a childhood cold sore from a genital infection.
• They cannot tell you when. Antibodies persist for life. A positive result says "at some point", not "recently", and cannot identify who you acquired it from.
• They take time to become positive. Antibodies develop over weeks after infection, so a test taken too early can be negative in someone who has just been infected.
• False positives happen. Particularly at borderline results, which is why a positive on a low-prevalence population can create more distress than clarity.

This is the honest reason herpes is generally not in the standard NHS screen: for someone with no symptoms, a blood test frequently produces anxiety rather than useful information. That is a considered clinical position, not an oversight or a cost-cutting decision — though it is rarely explained, which leaves people assuming they were skipped.

Is herpes included in a standard STI screen?

Usually not. A standard screen typically covers chlamydia, gonorrhoea, HIV and syphilis. Herpes is generally tested for when there are symptoms to swab, for the reasons above.

Can I test at home?

Home kits are available privately and are typically antibody blood tests, with the same limitations. A home kit cannot swab a lesion for you, so it cannot answer the question a swab answers.

My swab was negative but I still have symptoms.

A negative swab does not always rule herpes out, particularly if the sample was taken late in an episode or from a healing sore. If symptoms recur, being seen again early in the next episode is the sensible next step.

Can a test tell me who gave it to me?

No. And this deserves saying plainly, because the assumption causes real damage: the virus can lie dormant for years, so a new diagnosis does not establish when you acquired it, or from whom. Testing cannot settle that question, and treating it as though it can has ended relationships that did not need to end.