One of the most common questions/issues on this reddit - proper substrate

I have literally addressed the same issue about 5 times today. Either someone posts a picture of their animal on improper bedding (which either leads to education, or a pissing contest), or somebody posts a question about proper substrates. Here's a list to help you out. I'm not infallible, so I'll update this with anything that needs revision.

First and foremost, there's an excellent chance that the person at the pet store doesn't know what he/she is talking about. Same thing goes for the guy down the street that used to own an iguana 20 years ago. Improper substrates can lead to impaction, poor shedding, eye infections, and respiratory infections. All of these things can means expensive vet bills, and death.

Bearded Dragons, Leopard Geckos, and other arid lizards: slate tile (my personal favorite), reptile carpet, paper towels, or non-adhesive shelf liner. I've seen/read some people recommending alfalfa pellets (especially for beardies), but in my opinion these smell like shit and can harbor mold/bacteria. Uromastyx are also successfully housed on white millet/birdseed, but I think this option should be unique to the species.

Blue Tongue Skinks, terrestrial snakes, and most of burrowing reptiles that don't require tropical humidty: aspen shavings, cypress/orchid mulch, chemical-free soil (usually reserved for larger lizards like monitors and tegus)

Most frogs, planted terrariums, and tropical species: chemical-free soil, coconut coir (aka bed-a-beast)

Most arboreal snakes, geckos, lizards, etc.: paper towel, slate tile, reptile carpet, non-adhesive shelf liner, chemical-free soil, or coconut coir. The latter two, IMO, should be reserved only for enclosures with live plants or who's inhabitants require tropical humidity

You'll notice that I don't have sand, calci-sand, or ground walnut shells anywhere on my lists. That's because they're absolute shit.

That's off the top of my head - be sure to let me know if I've made any mistakes or should add anything.