A homestay host wants the Education Ministry to issue guidelines on sexual matters after catching his 45-year-old wife having sex with a teenage foreign student the couple were hosting.

The North Shore man - who did not want to be named - said he had contacted police after his wife's encounter with the 19-year-old South American, but was told they were powerless to help as the student was legally an adult.

"I'm at a total loss about what to do in such a situation and I'm bloody angry," the North Shore man told the Herald.

The man said he had faced issues in the past, where international students he hosted sneaked friends into the house late at night for sex.

"We really need to know what we can do in such situations, and I've suggested they add it to their pastoral care code. Is this something international students should be allowed to get away with?"

A compulsory code of practice for pastoral care was introduced in 2003 to protect the rights and welfare of international students.

The code is being reviewed by the ministry, and those involved with international students and the export education sector are being consulted.

Neil Scotts, senior manager at the Ministry of Education, said it had not received many submissions involving sexual matters and homestay families and students, but was unable to give exact figures.