Q and A


Does undetectable mean that someone is not infectious?

My boyfriend has HIV but he says he says he is undetectable.

Is it okay to have sex without a condom or do we need to use them?


Yes, having an undetectable viral load when on HIV treatment (ART) reduces the risk of transmission so low that this is generally thought to be not be infectious.

How low the actual risk goes is still being studied, but many researchers think that any risk gets so close to zero that it becomes so negligible as to not be important.

However, even if the risk is zero, no study can ever prove that tranmission is impossible. This is because science can never prove “a negative” – ie that somethinng will never happen.

Also, this answer discusses the research, but it is separate to your second question about what you and your boyfriend decide.

i-Base provide information for people to then make their own choices and decisions. Some people would find even a tiny theoretical risk is be too high. For others, exactly the same level of risk would be very acceptable.

So the decision on whether or not to use condoms is up to you. You should not feel pressured as you need to be happy with the choice you make.

A good example of when treatment prevent transmission is havin a baby when one partner is HIV positive and the other is HIV negative.

So long as viral load is undetectable, many couples where the man is positive and on treatment are conceiving naturally. When this was first suggested, the following guidelines were recommended.

  • The HIV positive partner should have an undetectable viral load for at least six months.
  • HIV meds should be taken as prescribed without missing doses.
  • Both partners should not have STIs.
  • Both partners need to agree to this.

This factsheet about the Swiss statement, explains this strategy in more detail.

More recently, the PARTNER study provides perhaps the most significant data that the risk of transmission might be zero. This study included more that 900 couples where one partner was positive and the other was negative. These couples were not using condoms.

After more than 58,000 times that couples had sex without using condoms, there were ZERO HIV transmissions. The HIV positive person had an undetectable viral load to be included in these results – but this could be for only one month rather than six months. This link has more information on the PARTNER results

A more detailed explanation on viral load and the risk of transmission is in this section of the i-Base guide on HIV transmission.

Even when the last viral load is undetectable on treatment, there are circumstances when transmission might occur. For example, if someone stops their meds or viral load rebounds for another reason. These situations are likely to be rare.

This answer was last updated in December 2016 from a question first posted on 26 January 2012.


  1. Lisa Thorley

    Hi Anda,

    Weight loss, though now rare can be a side effect of ARVs. What is it that you’re taking? How much weight have you lost?

  2. Anda

    I have been taking my meds for 2 month now but my weight continues to drop down. What can be the problem?

  3. Simon Collins

    Hi Mark – thanks for your comment.

    The i-Base website now has several thousand online Q&A’s and all answers have a caution on the published date. You were commenting on an answer from before the final PARTNER data were published, and the answer has been slightly revised to include this.

    i-Base have been pretty clear on the dramatic impact that having an undetectable viral load has on the risk of transmission. The Q&A on the PARTNER study used a pretty clear graphic to emphasise the results:

  4. Mark

    Further research and a consensus statement from dozens of health experts has shown that people with HIV who are on treatment and are undetectable are not transmitting the virus to their partners. We should say this, loudly and clearly. For more: http://marksking.com/my-fabulous-disease/five-reasons-hiv-undetectable-must-equal-untransmittable/