There are two primary reasons why we dry our hands after Netilat Yadayim.

The first reason is that the water remaining on the hands after washing may be considered impure and could contaminate the bread upon contact. The Gemara (Sotah 4b) explains that the Prophet Yechezkel cried out regarding this: “And Hashem said: ‘Even thus shall the children of Israel eat their bread defiled'” (Ezekiel 4:13). The Tur hints at this in the word “Lachmam” (their bread)—which can be read as “Lechem Mayim” (bread of water). Furthermore, the numerical value (Gematria) of “Lachmam Tamei” (their bread is defiled) is equal to that of “Belo Niguv Yadayim” (without drying hands). However, today, as we are blessed with an abundance of water and wash twice with a Revi’it (a specific measure), the initial water is rinsed away and the hands are pure.

The second reason for drying hands is brought by the Maharshal: so that the food does not become unappetizing (Nimas) due to the water on one’s hands. According to this reason, even when washing with a Revi’it, one must ensure the hands are completely clean and dry. As the Aruch HaShulchan (158:17) wrote, we have never heard of a permission to eat with damp hands.

Based on all the above, Maran the Chazon Ish (Siman 25:10) ruled that if a person waits until their hands are completely dry, there is no prohibition (as also ruled in Shu”t Betzel HaChachma 4:141). Consequently, an air dryer that dries the water completely is just as effective as a towel, and there is no restriction against using it.