If some EM waves can cook our food and others, e.g., x-rays and gamma rays, are hazardous, are microwaves generated by microwave ovens dangerous? In order to explore this question, we first need to answer the question of what happens when EM waves interact with matter? There are three ways that EM radiation can interact with matter. It can be transmitted, reflected, or absorbed. When the EM radiation passes through matter, if the matter is transparent and remains unchanged, then the EM radiation has been transmitted through the matter. If the matter is a very good reflector, then the EM radiation will not change except in the direction that it is travelling. In this case, the radiation is reflected. Absorption occurs when the electromagnetic radiation is absorbed by the matter and the EM radiation is transferred to the matter.26 This absorption can transfer energy from the radiation to the matter, resulting in an increase in molecular motions, such as the vibrational energy of particles in a solid, and translation, rotation, and vibration of molecules in liquids and gases. If the energy is high enough, chemical bonds may be broken and electrons can be excited to higher energy levels. Overall, absorption of EM waves results in an increase in the temperature of the absorbing medium.27
Are microwaves dangerous? Just like microwaves can cook food, they can cause burns on human flesh.28 The microwave oven door contains a metal mesh to prevent microwaves from exiting the oven but still allow light to escape.29 However, microwaves are not high enough energy to ionize atoms. To ionize atoms means to have enough energy to knock and electron free. Thus, EM energy that is high enough is known as ionizing radiation.30 Ionizing radiation includes higher frequency ultraviolet radiation, x - rays, and gamma rays. These types of radiation have enough energy to damage DNA and result in cancer.31 Microwaves do not carry enough energy with their much lower frequency microwaves and do not cause cancer.32
Just like microwaves, infrared radiation is a non-ionizing form of energy; however, this does not mean that it cannot be dangerous. Exposure to near, mid, and far infrared radiation can be damaging to both the eyes and skin. Infrared radiation may be experienced as heat and result in premature skin ageing and damage to the cornea, iris and lenses of the eyes.33