Experimental basis for discriminating between thermal and athermal effects of water‐filtered infrared A irradiation

Considering the widespread application of water‐filtered infrared A (wIRA) irradiation in medicine, cosmetics, and wellness, we have conluded that the biological effects of this electromagnetic spectrum, ranging from 780 nm to 1400 nm, have become an important focus of experimental research. Two main effects of wIRA on single cells are discussed: thermal effects, caused by absorption of energy by cellular water and the aqueous medium surrounding the irradiated sample that result in warming, and supposed athermal effects that result from a direct interaction of wIRA with cellular molecules/structures excluding water. In the following, we discuss different experimental setups and highlight some cellular responses to thermal and athermal wIRA effects, as well as the experimental problems in differentiating between them.