The Torah forbids causing a bloody wound in one's parent, or doing anything that results in the drawing of blood from a parent. The Rishonim (Medieval Halachic authorities) debate the question of whether this prohibition extends to situations where a son draws blood from his father for medicinal purposes. For example, may a physician perform an operation on his parent or draw blood for a blood test? This question arises in other situations, as well, such as if a parent wishes to donate blood, or if a parent has a splinter and asks the child to remove it, which often results in bleeding.

The Rambam (Rabbi Moshe Maimonides, Spain-North Africa, 1135-1204) held that in such situations, a child may perform the given procedure if nobody else is available to do so. By contrast, the Rif (Rabbi Yitzchak Alfasi, North Africa-Spain, 1013-1103) and the Rosh (Rabbi Asher Ben Yechiel, Germany-Spain, 1250-1327) held that under no circumstances may a child draw blood from a parent, even if nobody else is available. Despite the fact that the child seeks to draw blood for medicinal purposes, such as for a blood test or to remove a splinter, the Torah prohibition nevertheless forbids drawing blood from a parent.

The Shulchan Aruch (Yoreh Dei'a, 241:3; listen to audio for precise citation) rules that a child may not draw blood from a parent for medicinal purposes. The Rama (Rabbi Moshe Isserles, Poland, 1525-1572), in his glosses to the Shulchan Aruch, comments that where nobody else is available to perform the procedure it is permissible for a child to do so – in accordance with the Rambam's position. The Shulchan Aruch, however, makes no reference to such a distinction, indicating that he followed the stringent view of the Rif and the Rosh, forbidding drawing blood from one's parent even if nobody else is available to perform the required procedure.

Accordingly, Hacham Yishak Yosef (as cited in Yalkut Yosef – Laws of Honoring Parents, p. 539) ruled that it is forbidden for a child to draw blood from a parent for medicinal purposes, even if nobody else is available to perform the procedure. He added that this applies even if the parent granted the child permission to draw the blood.

Is it permissible for a child to shave his father's face? If, for example, the father is sick or elderly and cannot shave independently, may he ask his son to shave his face for him?

Hacham Yishak Yosef (ibid.) ruled that nowadays, when electric shavers are used, shaving is very unlikely to cause bleeding and it is therefore permissible for a child to shave his father's face. It is likewise permissible for a child to cut his father's hair. Hacham Yishak Yosef adds, however, that if the child uses a blade to trim the back of his father's neck, he must exercise particular caution to ensure not to cause any bleeding.

Similarly, it is permissible for a child to scratch his father's back, provided that he ensures not to cause bleeding.

If a person faints, Heaven forbid, is it permissible for his child to slap him on the face to wake him up?

Hacham Yishak Yosef (ibid. p. 553) ruled that since slapping does not entail any drawing of blood, a child may slap his father in such a case if nobody else is available to do so. If, however, there are other people available to wake the father, the son should ask them to slap the father rather than do so himself.

Summary: A child may not draw blood from his parent even for medicinal purposes – such as performing surgery, removing a splinter or taking blood for a blood donation or blood test – even if nobody else is available to perform the given procedure. A child may cut his father's hair, shave his face, or scratch his back, provided that he exercises caution to ensure that no bleeding occurs. If one's father fainted, he may slap his face to awaken him if nobody else is available to do so.