The Vatican has played down the importance of Pope Benedict's remarks appearing to temper the opposition of the Roman Catholic Church to condoms.
The Vatican spokesman said the pontiff's comments were not "revolutionary", but added it was the first time Pope Benedict had commented on the issue informally.
The Pope made clear in his view condoms were no answer to the Aids pandemic.
But he said their use could sometimes be justified in exceptional cases.
Vatican spokesman Fr Federico Lombardi said the Pope was speaking about "an exceptional situation" in one of the interviews in the book Light of the World: The Pope, the Church and the Signs of the Times, which is being published on Tuesday.
"The Pope considered an exceptional situation in which the exercise of sexuality is a real danger to the life of another," said Fr Lombardi.
Benedict used the specific example of a male prostitute using a condom to illustrate his apparent shift in position.
"The Pope maintains that condom use to lessen the danger of infection is a 'first assumption of responsibility,'" said Fr Lombardi, quoting from the book.
"In this, the reasoning of the Pope certainly cannot be defined as a revolutionary breakthrough".
BBC News
