1-Phenethylthiourea is a thiourea derivative primarily used in scientific research to study human and animal taste perception, particularly as a bitter tastant. It serves as a genetic marker for bitter taste sensitivity, where individuals with certain genetic variations (tasters) perceive it as intensely bitter, while non-tasters experience little to no taste due to differences in TAS2R bitter taste receptors. This compound is applied in sensory biology, pharmacogenetics, and nutritional studies to investigate taste mechanisms, population genetics of taste perception, and the development of food and pharmaceutical products tailored to taste variability.