What are the sources of molecular hydrogen in human breath?

Question

In the BBC News article [CES 2019: Tech preview of the expo's hottest new gadgets](https://www.bbc.com/news/technology-46715334) there is a new product that one can use to measure the hydrogen in ones breath, and this is supposed to have some connection to diet:>By contrast, FoodMarble's Aire measures the hydrogen in your breath and combines this with a log of what you have eaten, to warn you of foods you should avoid and possible substitutions.>Aire is designed to discover which foods are being passed to the large intestine without being fully digestedThere also exist [air quality monitor chips](https://www.sensirion.com/en/environmental-sensors/gas-sensors/) that measure both TVOC (total volatile organic compounds) and "eCO2", where "eCO2" is really a measurement of H2 in the air, and via some electronic algorithm uses it to calculate the expected rate that people are exhaling CO2.**Question:** Both of these are examples of interpreting the presence of molecular hydrogen as having some indication that we are alive, breathing and eating. Here I would like to understand the sources of hydrogen in human breath, and how that hydrogen makes it from source to breath.

Answer 1

Interesting question. Hydrogen is the most abundant element in the universe and its most common isotope is a single proton. So the name "hydrogen" and the term "proton" are essentially interchangeable.

Protons are incredibly important in biology. So important they have a specific unit of measurement associated with them. The pH scale is a measure of how much protons are in any chemical environment and range from 1 to 14, where 1 is incredibly acidic and 14 is incredibly basic and 7 is neutral (The pH of deionized water is 7).

The pH is a calculation that takes the negative base 10 log of the concentration of protons and provides an easy to interpret number for the acidity or basicity.

As mentioned before, protons are important to biology. All of life takes place in an optimal pH range and does not like deviations from that set point. All the proteins in your body and the microorganisms that inhabit your mouth and intestines have an optimal pH they like to live at.

Generally, the mouth is acidic thanks to the activity of those microorganisms producing lactic acid after they munch on all the leftover food in your mouth. These organisms love sugar, and will start producing acid like crazy when you consume sweets, degrading the enamel of your teeth. Diets heavy in grains and sugars would thus produce more acidic breath (higher concentration of protons) thanks to these bacteria.

Additionally, stomach acid is used to digest food and has the highest concentration of protons in your body (pH of around 2) so when you exhale some protons will inevitably be dragged along from here as well.

Brush your teeth!