Is fNIRS safe?

Very good, and important, question. Clearly fNIRS is employing frequencies of light that are purposely used to traverse the skull without much restraint, and this is in fact introducing exogenous stimuli. Well don’t fret, the amount of signal power using fNIRS can be comparable to sunlight. Further, of recent, several studies suggest there are various health benefits to infrared light stimulation at the cellular/metabolic level- even still these studies primarily employ chronic use.