Writing on one’s skin:
The Torah prohibits one from making a tattoo on his skin. It is clear from the Poskim that the Biblical prohibition only applies if the ink penetrates the inner layers of the skin and remains permanent. It is however unclear if there is a Rabbinical prohibition involved to write on the skin even if it does not penetrate the skin and will not remain permanent. Hence, leading to the question of whether one may write down a phone number on his hand. Another related question that comes up is with regards to whether one may place a tattoo sicker on one’s skin, or have makeup tattooed by one’s eyebrows and the like. This will be dealt with in a further Daily Halacha.
May one write on one’s skin?
- Example: One does not have paper and needs to write down a phone number, may he do so on his skin?
One who writes on his skin without making a cut in the skin which allows the ink to penetrate is exempt from Biblical liability. Nevertheless, some Poskim rule it is Rabbinically forbidden to do so. It is however unclear if this applies even with ink that is erasable. Other Poskim rule it is permitted to do so even Rabbinically. Practically, the widespread custom is to be lenient even initially. However, if the ink is permanent and cannot be removed at all from the skin even with the passing of time, one is to be stringent.
 See Minchas Chinuch Mitzvah 253/1; Nishmas Avraham Y.D. 180
 Michaber 180/1; Mishneh Makos 21a
 Minchas Chinuch ibid based on Beis Shmuel E.H. 124/16 “Even if the witnesses just wrote their signatures and did not fill it with ink, nevertheless they become Rabbinical Reshaim” [However see next footnote for alternative explanation of Beis Shmuel]; Implication of Rambam in Avodas Kochavim 7 who writes exempt; Implication of Tosafus Gittin 20b
 The law if the ink is erasable with time: The Minchas Chinuch ibid writes that even according to the stringent opinion, the Rabbinical prohibition is only regarding ink that is not erasable, however if the ink is erasable then the prohibition does not apply. So records also Shevet Halevi 3/111-1 in name of Minchas Chinuch. See however Pashegen Hakesav of Rav Chaim Kanievski p. 74-75 that such ink does not exist, as all writing on skin is erasable and hence one must conclude that according to the stringent opinion, any writing on the skin is Rabbinically forbidden. So is also implied from the Mishnas Chachamim brought in next footnote that according to the stringent opinion any writing is forbidden Rabbinically.
 Mishnas Chachamim 57; Kesef Mishneh on Rambam ibid; Shevet Halevi 3/111-1 that all the above Poskim in previous footnote, recorded by the Minchas Chinuch ibid only referred to one who made a cut into the skin and did not fill it with ink, in which case it is Rabbinically forbidden, however to simply write on the skin without making any cut was never discussed by them and there is thus no such source to Rabbinically prohibit it [Rav Chaim Kanievsky, brought in Nishmas Avraham ibid makes the same claim]; Implication of the Poskim who all omit the above Rabbinical prohibition against writing on the skin even without cutting it, including the Michaber 180, Chochmas Adam 89/11; Kitzur SHU”A 169/1; Ben Ish Chaiy Maaseiy 2/15
 Rav SZ”A, brought in Nishmas Avraham ibid, rules one may be lenient even initially; Rav Chaim Kanievsky, brought in Nishmas Avraham ibid that the Achronim write the custom is to be lenient; See Minchas Chinuch ibid that even according to the stringent opinion, if the ink is erasable it is permitted. [see previous footnotes]
 As rules the Minchas Chinuch ibid; To note however that to date there does not exist any ink that permanently remains on the skin with simply writing on it, without cutting into the skin with a needle and the like. If such a thing existed the entire tattoo industry would change to this method which is painless and woundless.