Terahertz (THz) radiation is a form of electromagnetic energy that has recently moved from the laboratory into public use, primarily for security purposes. This placement in everyday technology has naturally raised questions about its potential for harm. Because THz waves are not visible and are used to “see” through clothing, many people associate them with higher-energy, dangerous forms of radiation. This article explores the scientific facts regarding the nature of THz radiation, its common uses, and the current consensus on its biological impact.
Defining Terahertz Radiation on the Electromagnetic Spectrum
Terahertz radiation, often referred to as T-rays, occupies a distinct region in the electromagnetic spectrum between microwaves and infrared light. This frequency range typically spans from 0.1 to 10 terahertz, a transitional area that historically presented technological challenges for generation and detection. The energy level of THz radiation is its most defining safety characteristic, as it is classified as non-ionizing. This means the individual photons in a THz wave lack the energy to knock electrons away from atoms or molecules, a process called ionization. Ionization is the mechanism by which high-energy radiation, such as X-rays or Gamma rays, causes direct chemical damage to DNA and cellular structures.
Everyday Applications and Exposure Scenarios
The unique properties of terahertz waves—being non-ionizing while still penetrating many non-conductive materials—make them highly valuable for various applications. The most common exposure scenario for the general public is security screening systems, particularly the body scanners used in airports. These scanners use THz waves to create an image of a person’s body, revealing concealed objects like weapons or explosives hidden beneath clothing.
Beyond security, THz technology is rapidly developing for medical and industrial uses. In medicine, T-rays are being explored for non-invasive diagnostic imaging, such as detecting skin cancer, analyzing dental caries, and distinguishing between different tissue types. Industrial applications include quality control for pharmaceuticals, where the radiation is used to inspect the coating thickness of tablets, and non-destructive testing in manufacturing.
Biological Effects and Safety Assessment
The scientific investigation into the biological effects of terahertz radiation focuses on two primary mechanisms of interaction with human tissue: thermal and non-thermal effects. The most well-established interaction is the thermal effect, which is caused by the strong absorption of THz energy by water molecules in the body. Because the outermost layer of the skin, the epidermis, is rich in water, T-rays penetrate only to a very shallow depth, typically between 0.1 and 0.3 millimeters. This shallow penetration means that any absorbed energy is concentrated on the surface, primarily causing localized heating.
Current public exposure levels, such as those used in security scanners, are strictly regulated to ensure the heat generated is far below the threshold that would cause even minor thermal damage to the skin. For instance, safety guidelines for frequencies below 0.3 THz suggest public exposure limits in the range of 1 to 10 milliwatts per square centimeter to prevent excessive surface temperature rise. The second area of research involves potential non-thermal effects, which are significantly more theoretical and controversial. These studies explore whether THz radiation could subtly alter the function of biological macromolecules, such as changing protein folding or impacting DNA stability, even without causing heating. Some laboratory experiments using very high-intensity THz sources have suggested possible changes in gene expression or cellular stress markers.
However, these findings are often difficult to reproduce, and the observed effects are frequently associated with exposure levels far greater than those encountered in everyday life. Many studies have concluded that THz exposure does not affect cell viability, proliferation, or lead to DNA damage at relevant power densities. The prevailing scientific consensus, supported by regulatory bodies like the International Commission on Non-Ionizing Radiation Protection (ICNIRP), is that THz radiation, as used in current technologies, is biologically innocuous.