What should you never do with a baby's bottle?

Microwaving a baby's bottle is not recommended because it can create hot spots in the liquid, leading to uneven heating that may scald the baby's mouth. When a bottle is heated in the microwave, the liquid can heat much faster than the bottle itself, and these temperature variations can be dangerous when it is fed to the baby. Furthermore, microwaving can alter the composition of certain formula or breast milk, possibly reducing its nutritional quality.

In contrast, testing the temperature before feeding is a safe practice, as it ensures that the milk or formula is at a comfortable and safe temperature for the baby. Using bottles only at room temperature is also acceptable, and heating in boiling water, while it needs to be monitored carefully, is generally safer than using a microwave because it provides more even heat transfer.