Canon Law #998
The anointing of the sick by which the Church commends to the suffering and glorified Lord the faithful who are dangerously sick so that He relieve and save them, is conferred by anointing them with oil and using the words prescribed in the liturgical books.

Canon #1004
1. The anointing of the sick can be administered to a member of the faithful who, after having reached the use of reason, begins to be in danger due to sickness or old age.
2. This sacrament can be repeated whenever the sick person again falls into a serious sickness after convalescence or whenever a more serious crisis develops during the same sickness.