Infrared waves have a wavelength lower than the threshold of visibility on the electromagnetic spectrum, so we cannot see them. However, we can feel them as heat.
Welders have a risk of eye damage through infrared waves involved in the process of welding. If the eye is exposed to intense infrared waves, it can cause blindness. Goggles can be worn to prevent this. Infrared waves are used in therapy for muscle pain, but if the waves are too strong, they can cause skin burns. Infrared radiation can sometimes cause low blood pressure in the elderly. Lastly, excessive infrared radiation exposure can cause dehydration as the body loses water because of the heat.
Rather than being regarded as dangerous, though, infrared waves are more often than not considered useful.