Is masturbation sinful?

The Catechism of the Catholic Church affirms that the act of masturbation in itself is serious matter for sin. ' “The deliberate use of the sexual faculty, for whatever reason outside of marriage is essentially contrary to its purpose.” For here sexual pleasure is sought outside of the “the sexual relationship which is demanded by the moral order and in which the total meaning of mutual self-giving and human procreation in the context of true love is achieved” (2352).

Using one’s sexual powers outside of intercourse within marriage is disordered. It is self-love rather than love for a spouse and the fruit of married love. For anything to be a mortal sin, however, two other elements are required: sufficient freedom (wilfulness and consent) and knowledge or awareness. It is not always easy to judge how much freedom and consent  or awareness  are present in an act.

The Catechism says:

To form an equitable judgment about the subjects’ moral responsibility and to guide pastoral action, one must take into account the affective immaturity, force of acquired habit, conditions of anxiety, or other psychological or social factors that lessen or even extenuate moral culpability (2352).