It is not recommended to microwave other plastic bags if it is not labeled "microwave-safe." It is important to note that different types of plastics have different melting points and chemical compositions. Some plastics release harmful chemicals. In addition, you should pay attention to the recycling symbols on the plastic bags. Avoid using bags with recycling symbols 3 and 7. This is because they may contain chemicals like phthalates or bisphenol A (BPA), which can potentially leach into food when heated.