Explain that even though he has already had sex, it is ok to change his mind.
Suggest that he talk to a trusted adult.
The other options may offend a person
A. remove contaminants from people and equipment
decontamination: the process of cleaning an object or organism from contaminants and/or hazardous stuff/chemicals
Chancre
The first sign of syphilis is a small sore, called a chancre (SHANG-kur). The sore appears at the spot where the bacteria entered your body. While most people infected with syphilis develop only one chancre, some people develop several of them. The chancre usually develops about three weeks after exposure.