What is the only method that provides 100% effective protection against STIs through sexual contact?

Abstinence from sexual intercourse is the only method that guarantees 100% effective protection against sexually transmitted infections (STIs) that are spread through sexual contact. When an individual chooses to abstain from all forms of sexual activity, they eliminate any risk of contracting STIs that can be transmitted during sexual encounters.

The other methods listed can reduce the risk of STIs but do not offer absolute protection. Regular testing plays a critical role in early detection and management of STIs but does not prevent exposure. The use of condoms significantly lowers the risk of transmission but is not infallible, as condoms can sometimes break or may not provide coverage for all areas where infections can be transmitted. Limiting partners can also decrease the likelihood of exposure to STIs, but it cannot completely eliminate the risk if partners are untested or have an STI. Therefore, abstinence is the only method that ensures complete protection.