To ensure that your microwave bowls are safe to use, it is important to follow the manufacturer's instructions and use only materials that are specifically marked as microwave safe. It is also a good idea to follow proper safety precautions when using the microwave, such as never leaving it unattended while in use. If you have any concerns about the safety of your microwave bowls, it is a good idea to test them with a small, safe item before using them to heat larger items.