Only after the first boiled egg is cooked, it is no problem to cook it overnight. The same is true of tea eggs. Maybe you don't know that tea eggs are cooked twice. Boil it for the first time, crush it for the second time, and then cook it with tea and other auxiliary materials. Therefore, tea eggs must be cooked. However, tea contains biological acid and alkali components, which will penetrate into eggs after cooking and combine with iron in eggs; This combination is very irritating to the stomach. Over time, it will affect the digestion and absorption of nutrients, which is not conducive to human health.
Some people like to eat soft-boiled eggs. (The yolk is semi-liquid) That kind of egg can't be eaten overnight, even if it is cooked for the second time.