Above we defined chastity as a 'virtue of self-possession. It is about integrating one's sexuality into one's whole life as a human person. Being chaste means not being controlled by biological urges. Rather these urges or 'passions' are integrated into one's self-understanding as a sexual being made in the image of God who engages with other sexual beings who are themselves made in the image of God. Being chaste means taking control of one's desires and energies and directing them to those goods that are most rewarding, most meaningful, and that most support one's own flourishing and the flourishing of others.' Consequently, the Catholic perspective also highlights a number of so-called 'sins against chastity'. In other words, these are actions and their associated intentions which involve choosing not to direct one's sexuality, including its emotional and physical components, to those goals or ends that are most good for human flourishing, both of oneself and of others. In addition to masturbation and fornication (sex before marriage), these include lust, prostitution, incest and rape. What follows quotes directly from the Catechism of the Catholic Church (para. 2351–2356) and should be seen in light of the foregoing discussions on chastity and what is truly good. Lust is disordered desire for or inordinate enjoyment of sexual pleasure. Sexual pleasure is morally disordered when sought for itself, isolated from its procreative and unitive purposes. Pornography consists in removing real or simulated sexual acts from the intimacy of the partners, in order to display them deliberately to third parties. It offends against chastity because it perverts the conjugal act, the intimate giving of spouses to each other. It does grave injury to the dignity of its participants (actors, vendors, the public), since each one becomes an object of base pleasure and illicit profit for others. It immerses all who are involved in the illusion of a fantasy world. It is a grave offense. Civil authorities should prevent the production and distribution of pornographic materials. Prostitution does injury to the dignity of the person who engages in it, reducing the person to an instrument of sexual pleasure. The one who pays sins gravely against himself: he violates the chastity to which his Baptism pledged him and defiles his body, the temple of the Holy Spirit. Prostitution is a social scourge. It usually involves women, but also men, children, and adolescents (The latter two cases involve the added sin of scandal). While it is always gravely sinful to engage in prostitution, the imputability of the offense can be attenuated by destitution, blackmail, or social pressure. Rape is the forcible violation of the sexual intimacy of another person. It does injury to justice and charity. Rape deeply wounds the respect, freedom, and physical and moral integrity to which every person has a right. It causes grave damage that can mark the victim for life. It is always an intrinsically evil act. Graver still is the rape of children committed by parents (incest) or those responsible for the education of the children entrusted to them.

In case of rape a Catholic perspective permits the use of means to prevent fertilisation where there is no danger of causing an abortion. The Catholic perspective, however, does not permit the abortion of an embryo already conceived. For this reason, it is very important that people seek help as soon as possible after the rape. The logic of the Catholic argument is as follows. Whilst contraception is not permitted in the case of a loving married couple because this would defeat the purpose of marriage, in the case of rape a very different relationship exists between the two parties. The woman who has been raped has not freely chosen to have sexual intercourse with her attacker and indeed has been violated against her will by an aggressor. A person is always allowed to defend themselves against such an attack. Preventing the possible fertilization of one of the woman's ova by the attacker's sperm is a legitimate part of this defence against the attacker. Therefore, medications which specifically work to prevent fertilization can be administered. What may not be administered are medications that have an abortive effect resulting in the destruction of an already fertilized egg, which is now an embryo. Once fertilization has taken place, the newly formed embryo is considered an innocent human life, a human being worthy of the same respect as all other human beings.