The plate in a microwave that is labeled "for use in microwave only" is designed and manufactured to be microwave-safe. This label indicates that the plate has undergone specific testing to ensure that it does not pose a risk when used in a microwave oven and that it can withstand the conditions inside a microwave during the cooking or heating process.
The reason for this label is related to the materials used in the plate's construction. Microwave-safe plates are typically made of materials that do not absorb microwave radiation, do not react to the heat generated by the microwave, and do not leach harmful substances into the food.
Some materials, like certain types of ceramics, glass, and plastics, can crack, melt, or release toxins when exposed to the high temperatures produced inside a microwave oven. By using a plate specifically designated as microwave-safe, you can reduce the risk of accidents, such as the plate shattering or the food being contaminated with harmful substances.
If a plate is not labeled as microwave-safe, it is safer not to use it in the microwave to avoid potential hazards. When in doubt, always check the manufacturer's instructions or use microwave-safe alternatives.