Human reaction to Capsaicin and Scoville Heat Units

At ZP FoodSense we have the world's only fast test for objectively measuring the hotness of chilli products.


On this page we summarize a scientific paper where they link the subjective burn sensation people experience when eating chilli products to the objective measurement of the capsaicin concentration in products.



We also provide a calculator for connecting the human perception of chilli burn and Scoville Heat Unit.

The article below is based on the research of our academic colleagues.

Scoville Heat Units

In this article we summarise a scientific paper that helps connect the subjective experience of burn from chillies with the objective measurement of capsaicin concentration in the product, at the end of this article we also provide a calculator for converting between Scoville Heat Unit and perceived burn.

 Scoville heat units (SHU) is a measurement of the number of times capsaicin needs to be diluted by sugar-water before the sensation of hotness is lost.


The number of Scoville Heat Units (SHU) in a pepper indicates the amount of capsaicin present. The higher the Scoville rating, the hotter the pepper.


The Scoville Organoleptic Test is a refined, systematic approach that was the first laboratory test used to measure heat in chile peppers.


The samples are diluted in the laboratory until heat can no longer be detected by the tasters. 


•Capsaicin is an active component of chili peppers, plants belonging to the genus Capsicum. It is a chemical irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact.


•Capsaicin molecules activate certain neurons responsible for the perception of pain. Neurons send a message of heat to the brain, whether the cells are activated by an actual burn or by a hot pepper. They are non-distinguishable from each other in this way.


•If people inherit fewer capsaicin-detecting receptors, it makes them less sensitive to the irritating compound in spicy foods. 


•Regular chili pepper intake can result in capsaicin desensitization.

The Experiment

Participants in an experiment rated the burning and bitterness of capsaicin and other non-sample related items on a horizontal general labelled magnitude scale (gLMS). The scale is labelled at 0 with “NS’ (no sensation) to ‘the strongest imaginable sensation of any kind’ at 100. Labels were placed at 1.4, 6, 17, 35 and 51 (‘BD’; barely detectable, ‘weak’, ‘moderate’, ‘strong’ and ‘very strong’; respectively).

Formula for burn level

This paper includes a formula that can be rearranged to determine the concentration required for a specific desired level of burn:


In the adjacent graph we have shown how the burn experience changes with Scoville Heat Unit (SHU), and we have included Tabasco Sauce as a reference point.


The shape of the graph above shows that as the SHU increases the ability of the human to perceive an increase in true hotness /capsaicin concentration diminishes; the ability of the human to accurately perceive SHU has become saturated.


From a scientific perspective this idea that the human perception of hotness becoming saturated does fit with the idea that taste is in part linked to receptors to which molecules like capsaicin binds, and as there is a finite number of receptors they will inevitable become saturated.