Acids, in themselves, affect sensory systems in four different ways. In the mouth, they impact taste receptor cells, which detect sourness, and the trigeminal system, which is sensitive to chemical irritation. Examples of the latter include extremely sour candies or the dryness or astringency from tannins and certain acids.
In the nasal cavity, aromas are detected by olfactory receptor cells while volatile chemical irritants, such as those associated with horseradish, affect the nasal trigeminal system. All acids have an oral impact but only some have a nasal impact.