Used correctly and consistently, external (male) and internal (female) condoms are highly effective at reducing transmission of STIs that spread through bodily fluids - including HIV, chlamydia, gonorrhoea and trichomoniasis.
However, condoms cover only part of the genital area, so infections spread by skin-to-skin contact - genital herpes, HPV (genital warts), and syphilis sores - can still pass through contact with areas the condom doesn't cover. Condoms reduce but do not eliminate this risk.
For fuller protection, combine condoms with other measures: HPV vaccination, hepatitis B vaccination, HIV PrEP where appropriate, regular testing, and open conversations with partners. A licensed doctor or pharmacist can advise on which preventive options fit your circumstances. Condoms also remain one of the few methods that protect against both STIs and pregnancy.