U=U: Undetectable = Untransmittable

U=U means Undetectable = Untransmittable. It is one of the most important messages in the modern HIV response, and it is backed by strong scientific evidence.

What "undetectable" means

"Viral load" is the amount of HIV in the blood. Antiretroviral therapy (ART) lowers this amount. When it falls so low that laboratory tests can no longer measure it, it is called an undetectable viral load.

Reaching an undetectable load usually takes a few months of correct treatment.

Why "undetectable" means "untransmittable"

Large studies of thousands of couples have shown clearly: a person with HIV who has an undetectable viral load does not transmit the virus to their partner through sex. The risk is effectively zero.

This is the U=U principle.

Why it matters so much

• For people with HIV: it removes the fear of transmitting the virus; it allows relationships, intimacy and family planning without anxiety.
• For partners: it provides reassurance and confidence.
• Against stigma: it dismantles the false idea that a person with HIV is a "danger". With treatment, they are not.
• For public health: treatment becomes prevention — the more people who are undetectable, the fewer new infections.

Conditions for U=U to work

• adherence: medication must be taken daily, as prescribed;
• monitoring: regular viral-load checks to confirm it stays undetectable.

U=U refers to sexual transmission. For other situations (for example sharing needles or breastfeeding), talk to your doctor about additional measures.

The key message

Treatment works. A person with HIV who takes their treatment correctly can live healthily and does not transmit the virus. See the Living with HIV and About HIV pages.