Always use condoms during sex and never share needles

30. Always use condoms during sex and never share needles

Cost: A single condom costs just one or two yuan. The challenge isn’t the price, but making sure to use one every single time — and putting it on right from the start.

In plain terms: Using a condom every time throughout sex cuts the chance of HIV transmission between heterosexual partners by roughly 70% or more. “Most of the time” just isn’t enough — that still leaves the risk nearly as high as not using one at all. Condoms also protect against syphilis, gonorrhea, and other STIs.

Benefit: One study pooled data from 25 separate studies involving 10,676 heterosexual couples in which one partner was HIV‑positive and the other was not. Compared to couples who never used condoms, those who consistently used them saw their HIV transmission risk drop by about 71%. The reported relative risk was 0.29, with a 95% confidence interval of 0.20–0.43. When compared to couples who used condoms only intermittently, the risk was lower by roughly 77% (RR = 0.23; 95% CI 0.13–0.40). The authors concluded that although condoms are not perfect, “consistent use can reduce HIV transmission by more than 70%.” This same level of protection also applies to syphilis, gonorrhea, chlamydia, and other sexually transmitted infections.

Evidence grade: A

Sources: Giannou FK, Tsiara CG, Nikolopoulos GK, et al. (2016). Condom effectiveness in reducing heterosexual HIV transmission: a systematic review and meta-analysis of studies on HIV serodiscordant couples. Expert Review of Pharmacoeconomics & Outcomes Research, 16(4), 489-499. <https://doi.org/10.1586/14737167.2016.1102635>; Fonner VA et al. (2016). Effectiveness and safety of oral HIV preexposure prophylaxis for all populations. AIDS. <https://doi.org/10.1097/QAD.0000000000001145> ( PrEP)

Notes: The difference between “infrequent use” and “no use” is minimal; the whole benefit hinges on the phrase “every time, throughout.” Sharing needles is a separate, highly effective route of transmission that has nothing to do with sex — this includes drug injection, tattooing, and piercing. For people at high risk, pre‑exposure prophylaxis (PrEP) offers another option: taking medication in advance to block infection. Pooled data from 18 studies show that when at least 70% of participants adhered to the regimen, PrEP cut HIV risk by about 70% compared to placebo (RR = 0.30; 95% CI 0.21–0.45). Trials with lower adherence rates showed no protective effect. PrEP is a prescription medication; consult an infectious‑disease specialist or public‑health clinic rather than ordering it online. Information on what to do after potential exposure can be found in Section 13.