We cannot see ultraviolet (UV) light but it can have hazardous effects on the human body. Ultraviolet light in sunlight can cause the skin to tan or burn. Fluorescent substances are used in energy-efficient lamps - they absorb ultraviolet light produced inside the lamp, and re-emit the energy as visible light. Similar substances are used on bank notes to detect forgeries. The hazardous properties of UV mean it will kill bacteria and can be used for disinfecting water.
Changes in atoms and their nuclei can cause electromagnetic waves to be generated or absorbed. Gamma rays are produced by changes in the nucleus of an atom. They are a form of nuclear radiation. High energy waves such as X-rays and gamma rays are transmitted through body tissues with very little absorption. This makes them ideal for internal imaging. X-rays are absorbed by dense structures like bones, which is why X-ray photos are used to help identify broken bones.
X-ray imaging is also used for scanning the internal structure of objects and in airport security scanners.
Gamma rays are used for sterilising food and medical instruments, and in the treatment and detection of cancer.
Ultraviolet waves, X-rays and gamma rays are types of ionising radiation. They can add or remove electrons from molecules, producing electrically charged ions. Ionisation can have hazardous effects on the body: