Even though infrared (IR) light is sometimes referred to as IR "radiation," it is not particularly harmful in most cases. This is because, unlike more powerful forms of radiation, IR light only has enough energy to start molecules moving, not to break them apart or otherwise cause damage. When somebody absorbs IR light the only consequence is usually that the person feels warmer. However, it is true that in some rather rare cases IR can indeed be hazardous.
Electromagnetic radiation is a form of energy which can be thought of as a wave which moves through space. Electromagnetic waves have different frequencies, ranging from very low frequencies such as those which make up radio waves, to very high frequencies as in X-rays. Somewhere in the middle are the wavelengths which our eyes can detect and which make up the visible spectrum spanning the colors red to violet. Higher frequency radiation has more energy and can thus interact more strongly with matter that it encounters. This is why we can be constantly exposed to radio waves with no ill effects but even relatively brief exposure to X-rays can be hazardous.
Infrared radiation is a form of electromagnetic radiation which is found just outside the visible portion of the spectrum, before the color red. Infrared radiation is invisible but the energy of this region happens to correspond to the approximate level of energy needed to start molecules moving in various ways. For example, wavelengths in the middle of the IR region are able to start various portions of molecules vibrating. IR light, which has even less energy than visible light, does not have enough energy to damage molecules in the way that higher energy waves such as X-rays do.
Safety Hazards of Infrared
Since IR radiation only works to get molecules moving, any moderate dose of IR radiation will simply heat up any living tissue it touches upon. The only hazard in most cases is that prolonged exposure to a very high level of IR could result in a burn, just as could exposure to a hot stove or any other heat source. The one exception is that workers who are exposed to close-up, high levels of IR over many years, such as those working with molten glass or steel, have been found to have increased incidences of eye cataracts as a result.
One unusual form of IR radiation which can be immediately hazardous is a particular type of laser pointer. Most handheld laser pointers sold to consumers are intrinsically safe since, if someone accidentally looks into the laser, they will instinctively shut their eyes in response to the bright light before eye damage can occur. However, tests have shown that some inexpensive laser pointers which emit green light also emit invisible IR laser light at a level powerful enough to cause eye damage. Since the IR light is not visible it does not cause a blink reflex and thus these lasers could potentially be harmful.