HIV testing and risks of sexual transmission

This guide to HIV testing and HIV transmission was updated in December 2019.

Main changes since the previous edition are based on:

  • U=U: how an undetectable viral load on ART stops HIV transmission, and
  • PrEP: how effectively PrEP also prevents transmission.

This guide was produce to answer all questions on transmission risk and HIV testing.


HIV in the UK

HIV basics

Ways that HIV is not transmitted

Risks for transmission

HIV testing: feelings of fear, anxiety and guilt

Frequently Asked Questions (FAQs)

PrEP (Pre-Exposure Prophylaxis)


U=U: Undetectable = Untransmittable

HIV testing

Skin, mucous membranes and HIV transmission

Timeline for immune responses and testing

Additional sections


Further information and links




Tables, diagrams and illustrations


This guide was written and compiled by Simon Collins for HIV i-Base with appendices written by Charlotte Walker.

First edition February 2012.
Second edition February 2013.
Third edition July 2016.

Thanks to the community and healthcare professional advisors for comments including Dr David Asboe, Bisi Alimi, Polly Clayden, Paul Clift, Nathan Geffen, Li Marhaban, Angelina Namiba, Emma Rezel, Memory Sachikonye, Tracy Swan, Matt Williams.

Thanks to Monument Trust and MAC AIDS Fund for supporting this publication.

About our guides

Information about how we produced this guide and the importance of using language that is direct and easy to understand.

This includes information on how to write non technical medical information that may be useful as a resource for other organisations.

Cover: Untitled, 1984 © Keith Haring Foundation. Used with permission.

Last updated: 1 December 2019.