it, usually because of some unfamiliar aspect of the food or beverage, including bitterness, a strong or strange odor, taste, or appearance. clinical significance patients with addison's disease, pituitary insufficiency, or cystic fibrosis sometimes have a hyper-sensitivity to the five primary tastes. disorders of taste ageusia (complete loss of taste) hypogeusia (reduced sense of taste) dysgeusia (distortion in sense of taste) hypergeusia (abnormally heightened sense of taste) viruses can also cause loss of taste. about 50% of patients with sars-cov-2 (causing covid-19) experience some type of disorder associated with their sense of smell or taste, including ageusia and dysgeusia. sars-cov-1, mers-cov and even the flu (influenza virus) can also disrupt olfaction. history in the west, aristotle postulated in c. 350 bc that the two most basic tastes were sweet and bitter. he was one of the first persons to develop a list of basic tastes. research the receptors for the basic tastes of bitter, sweet and savory have been identified. they are g protein-coupled receptors. the cells that detect sourness have been identified as a subpopulation that express the protein pkd2l1, and the responses are mediated by an influx of protons into the cells. as of 2019, molecular mechanisms for each taste appear to be different, although all taste perception relies on activation of p2x purinoreceptors on sensory nerves.