Are onions poisonous to humans if cut open and left out over night?

Onions are not poisonous if cut open and left out overnight. On the contrary, some cultures and dishes call for precisely that. However, it is essential to note that leaving cut onions out for extended periods can attract bacteria due to the high moisture content. Cooked or grilled onions should not be left out overnight, as they are even more susceptible to bacterial growth.

Always follow proper food handling practices to ensure the safety of your food. If in doubt, it is always best to discard any food that has been left out for an extended period.