I have heard of hatchling mountain kingsnakes having an issue. It really depends on how you use it. Any really tiny snake can be affected.

I have used it on many snakes - cornsnake hatchlings, rosyboa adults and neonates, ball python neonates, spotted pythons, etc. To date, no problems. I spray the cage, let it dry completely, then add substrate and snake. No water for 24 hrs. Then I spray the floor around the cages.