What is the ruling on the clothes a man wears during intercourse, and are they ritually impure and must be changed?

The preponderant opinion is that semen is pure, whether it is the semen of a woman or the semen of a man. Therefore, if the clothes worn by the man during intercourse were only soiled by semen, they are pure, and there is no need to change them, though it is recommended to wash the semen off. However, if they were soiled by pre-seminal fluid (madhi), they must be purified, because it is impure.