Why does pepper make us sneeze?

Just as dust irritates sensitive noses, it is the finely ground powder of peppercorns that triggers an irritation response

If you spend any time in the kitchen, chances are good that the peppercorn powder has likely caused you to sneeze once or twice, forcing air out of your nose at about 161 km per hour!
Peppercorns, whether whole, crushed or powdered, are a commonly used spice in almost every cuisine of the world. The peppercorns we eat are actually fruits of the Piper nigrum plant, which is part of the Piperaceae family, a flowering vine native to the tropical and subtropical regions of India. Piper nigrum is the most common source of black pepper.

There are many organic compounds present in pepper giving it that typical pungent odour and its tasty properties. Almost 600 compounds have been isolated and identified from black pepper thus far! One of these compounds is responsible for triggering the sneeze reflex.

The main component of black pepper, which makes it spicy and pungent, is piperine. This alkaloid (organic compound containing nitrogen) is what makes pepper one of the most widely used spices in the world. The concentration of piperine per peppercorn varies, depending on the strain of the pepper, between 2% and 7.4% of its constituents. Naturally, the higher the piperine content, the greater the resultant irritation in the nose, meaning a more intense bout of sneezing.

Piperine engages certain receptors in the nose and irritates nerve endings. When these receptors are stimulated, they trigger a biological reflex response to push out the irksome pepper that has gotten inside. Sneezing is basically a defensive response to ensure that the nose and the receptors are free from the discomfort of piperine as fast as possible. This is how our noses ‘scratch themselves from the inside’, so to speak.

Just as dust irritates sensitive noses, it is the finely ground powder of peppercorns that triggers an irritation response. When the piperine is bound in the whole peppercorn, it cannot enter the nose nor interact with the receptors. However, grinding the peppercorns to a fine dust releases the piperine into the air and the fine dust of pepper further exacerbates the irritation, simultaneously triggering an extensive number of olfactory receptors that then induce a sneeze.