Incubation period
2 to 4 weeks for the first short illness, if it happens at all.
When a test becomes reliable
A modern fourth-generation lab test is reliable from about 18 to 45 days. A home antibody test can take up to 90.
Symptoms
- 2 to 4 weeks in: fever, sore throat, rash, headache, swollen glands, aching muscles — easy to mistake for flu
- Then, commonly, years with no symptoms whatsoever while the virus is still active and still transmissible
- Later: infections and illnesses that a healthy immune system would have shrugged off
Good to know
- Undetectable equals untransmittable: someone on effective treatment with no detectable virus in their blood cannot pass HIV on sexually. This is settled science, confirmed by studies following thousands of couples
- Because the early illness looks exactly like flu, it is missed almost every time
- Testing negative too early is the common mistake — the window period is why a test three days after a risk means nothing
- It is not passed on by kissing, sharing cups or living together
How it was discovered
In 1981 doctors in Los Angeles and New York started seeing pneumonias and cancers that only appeared in people with no immune defence. The virus behind it was isolated in 1983 at the Institut Pasteur by Françoise Barré-Sinoussi and Luc Montagnier, working with a lymph node sample from a patient, and independently confirmed in the United States. Barré-Sinoussi and Montagnier shared the Nobel Prize in 2008.
Last updated: September 2026
This page is general information, not a diagnosis and not medical advice. Symptoms overlap between infections, and many infections have none at all — only a test can tell. If you think you have been exposed, talk to a doctor.