Most are fuel/technical/food grade denatured ethyl alcohol (ethanol) with glycerin (glycerol) as a humectant/thickener. IPA is allowable but more expensive.
A number of them have been made from the heads and tails of normal spirit distillation process (which are waste products), or are distilled with other organic waste products (like dog food process waste), which often smell awful and are super sticky.
I bought a gallon of some stuff early into the pandemic from a online retailer that sells commercial fog machine supplies. It smells likes farts. I felt bad giving bottles of it to friends and family but it wasn't like there was much else available on the shelves and at the time touch contamination was still a big concern. I added some fragrances so it smells mostly like lemons now and only a hint of farts.
We bought another gallon from a cosmetics supply wholesaler and it was much less stinky.
A number of them have been made from the heads and tails of normal spirit distillation process (which are waste products), or are distilled with other organic waste products (like dog food process waste), which often smell awful and are super sticky.