Harmful Effects

When electromagnetic radiation becomes harmful

All electromagnetic waves transfer energy from a source to an absorber. When body tissue absorbs that energy, it may become warmer or its cells may be damaged. The effect depends on the type of radiation and how much exposure occurs.

The specification refers to excessive exposure. Harm is generally more likely when radiation is more intense or exposure lasts longer, because more energy can be transferred to the body. Frequency also matters: higher-frequency radiation has more energy in each packet and can cause different kinds of damage. A radiation therefore has a particular hazard, while the risk in a real situation also depends on the exposure.

Microwaves: internal heating

Microwaves can be absorbed by body tissue. Their transferred energy increases the movement of particles, raising the tissue's temperature. Excessive exposure can therefore cause internal heating of body cells.

This is a heating effect rather than an ionising effect: microwaves do not have enough energy in each packet to remove electrons from atoms. Nevertheless, non-ionising does not mean harmless. Sufficient energy transfer can still damage living tissue through heating.

Infrared: burns at the skin

Infrared radiation transfers energy by heating. When excessive infrared is absorbed by the skin, its temperature rises and it can cause skin burns.

Keep this distinct from the microwave effect required here: infrared is associated with burns to the skin, whereas microwaves are associated with internal heating of body cells.

Ultraviolet: damage to surface cells and eyes

Ultraviolet radiation has a higher frequency than visible light. Excessive ultraviolet exposure can damage surface cells, especially skin cells, and can also damage the eyes.

Damage to a cell's genetic material can produce a mutation. If mutations disrupt the control of cell division, cells may divide uncontrollably, so ultraviolet exposure can lead to skin cancer. Damage to the eyes can lead to eye conditions. These effects may develop after exposure rather than being felt immediately.

X-rays and gamma rays: mutation and cell damage

X-rays and gamma rays are very high-frequency electromagnetic radiations. They are ionising: when absorbed, they can remove electrons from atoms and form ions. Ionisation can disrupt important molecules within cells.

Consequently, excessive exposure to X-rays or gamma rays can cause mutations or other damage to cells in the body. A damaged cell may die, work incorrectly or, if its genetic material is altered, carry a mutation when it divides. This explains why exposure must be carefully controlled even though these radiations also have valuable uses.

Comparing the four effects

The essential pattern is:

• microwaves: internal heating of body cells;
• infrared: skin burns;
• ultraviolet: damage to surface cells and eyes, which can lead to skin cancer and eye conditions;
• X-rays and gamma rays: mutation or damage to cells in the body.

Microwaves and infrared mainly cause harm through heating. Ultraviolet, X-rays and gamma rays can damage cells more directly; X-rays and gamma rays are strongly associated with ionisation. In every case, the requirement concerns excessive exposure, not the idea that any encounter automatically causes the listed harm.