Does vape liquid need a hechsher?

Answer: Yes.

Reason: The liquid needs kosher certification. Steam from a food is treated like the food itself, so inhaling the vapor is like eating the liquid. Some poskim hold it does not need a hechsher, but use only one with a hechsher if possible. Many poskim also hold smoking is forbidden because it damages health.

Source:

• Rabbi Moshe Shaul Klein, Rabbi Moshe Sternbuch, Rabbi Azriel Auerbach. Gilyon Meir Derech (20, 23); Gilyon Omek HaPshat (206).
• cRc: vape juice is “not recommended for health reasons” (Shulchan Aruch, Choshen Mishpat 427:9–10) and also poses standard kashrus issues which demand hashgachah.

Related questions:

• Does Listerine spray need a hechsher? Yes.
• Do fruit or herbal extracts need a hechsher? Yes.

More from Rabbi Tahan: Q&A: Kashrut for a Vape · Q&A: Hechsher on Electronic Cigarettes

References: cRc (askcrc.org), “Vape Juice” · cRc (askcrc.org), “Electronic Cigarette”