Q9.
What protective devices can be used during sexual activity to reduce the spread of STIs?
Answer
Barrier devices — condoms, and vaginal covers (female condoms). These are the only contraceptive methods that also protect against sexually transmitted infections.
Why a barrier works against infection while a pill does not: the organisms that cause gonorrhoea, syphilis, herpes, genital warts and HIV are carried in body fluids and passed on during close physical contact. A condom is a physical sheet between the two people, so those fluids are not exchanged and the organisms have no route across. A pill changes hormone levels inside one person's body; it does nothing whatever to the exchange of fluids, so it cannot block transmission.
The chapter names the infections concerned: gonorrhoea, herpes, syphilis, genital warts and HIV (which can eventually lead to AIDS). It also makes the point that some of these are not curable yet — which is exactly why prevention matters so much more here than treatment.
Tip: a barrier reduces risk sharply but does not reduce it to zero. Some infections can spread from skin the device does not cover. The complete answer is: use a barrier device, avoid unsafe contact, and if there is any doubt see a doctor early — several STIs are curable if treated promptly and are far harder to deal with later.