They're used in the alchemy place in the underground, but I think you need to be a zombie to use that.
The zombie skins come from the Survival/Pandemic event in February, so if you missed out on that then you'll have to wait until next year before you can become one and access the place.
Do the temporary vials count as a zombie for that period or no? I am leaning towards no but I don't know.
I thought about mentioning that, but I actually don't know either.
If i remember correctly, back before we could keep multiple skins, I got a couple of days access to the alchemist when I used the on myself. It took two or three days for the infection to progress enough for access, and then I only had a few days before it started to fade away.
if you want to mess with the icky vials to see if they allow access, they are
Vaguely Sticky Vial Stinging Vial Lotus Vial Creeping Vial Bulbous Vial
These are all made with human/subetan organs and their infections are not curable in any way. As the disease runs it course, you will get better on your own with time.