In 1912, G. H. Parker described the sensory system responsible for detecting chemical irritants as “the common chemical sense.” Although Parker noted that the common chemical sense was mediated by irritant-detecting free nerve endings resembling pain receptors, he concluded that it was a separate sense with its own set of receptors that produced distinct sensation qualities different from taste and smell. Free nerve endings are axons that do not terminate in specialized structures and are devoid of myelin (fatty insulation around axons). Today, we know that the nerves that respond to chemical irritants do not constitute a separate, independent sense, as Parker hypothesized. Rather, they are part of the general somatic sensory system: a subset of pain and temperature sensitive fibers that can be found ...