No. Yogurt is a perishable dairy product, and overnight at room temperature goes far past the 2-hour safety limit — even if it still looks and smells like yogurt.
Yogurt already contains live cultures, which makes some people assume it is more resistant to spoilage than other dairy — but those cultures do not protect it from the harmful bacteria that can also grow once it warms up.
The tangy smell of yogurt also makes it harder to tell by sniffing whether it has actually gone bad, which is exactly why the time limit matters more than your nose here.
Yogurt needs refrigeration at 40°F or below, and like other dairy, it should not sit at room temperature longer than 2 hours. Its own beneficial bacteria do not reliably outcompete harmful bacteria like Listeria or Staph, especially once the container has been opened.
Serve only the portion you will eat, and return the rest to the fridge right away rather than leaving the tub out for a snack later. If you are packing yogurt for lunch or travel, use an insulated bag with an ice pack.
A sealed, shelf-stable yogurt drink is a different product with its own preservation method — check the label. Standard refrigerated yogurt, opened or not, follows the 2-hour rule once it is out of the fridge.
Overnight is too long for yogurt at room temperature, sealed or not. When in doubt, toss it and grab a fresh container rather than risk it.
No — that is already double the USDA's 2-hour limit for perishable dairy. Discard it to be safe.
Slightly — an unopened tub has a bit more protection, but standard refrigerated yogurt should still not sit out more than 2 hours.
No — freezing stops further bacterial growth but does not remove bacteria or toxins already present, so yogurt left out too long should be thrown away, not frozen.
No — Greek yogurt is still a perishable dairy product and follows the same 2-hour room-temperature limit.