IINM, an e-liquid/E-juice consists of propylene glycol (PG) , vegetable glycerin (VG), food flavorings, and (optionally)nicotines. google it.
i wouldn't say it's 100% safe. but comparatively to traditional tobacco (which has around 4000 chemicals). i'd say yes.
that's why it was intended for people who smokes. not some trends or accessory.
just my 2 cents.