What factors cause a high CO reading?

Why is my device showing a high CO reading?

Smoking – as you would expect, smoking is the main reason for a high CO breath reading and for that reason the CO breath test is seen as the overall best way to validate smoking status and track progress during a quit attempt.

Cannabis/marijuana – regardless of the THC (delta-9-tetrahydrocannabinol) level the levels of carbon monoxide absorbed are three to five times greater than among tobacco smokers(1). This may be due to the marijuana users inhaling more deeply and holding the smoke in the lungs and because marijuana has a very high burning temperature compared to tobacco.

Hydrogen – all electrochemical sensors for CO have a certain amount of cross-sensitivity with hydrogen, this means that if there is hydrogen in the breath sample the sensor will see this as CO therefore increasing the reading. Hydrogen is produced in the gut normally in very low concentrations (5-25ppm), but if you have an intolerance to sugars such as lactose or fructose you will produce higher levels of hydrogen after eating one of these sugars. Bedfont have spent years working with our sensor partners to ensure the lowest possible cross-sensitivity to hydrogen and as a result the iCOquit has a cross-sensitivity of less than 10%. Therefore even for a very unusually high level of hydrogen on the breath such as 100ppm, the maximum level of ppm added to the reading would be 10ppm on the iCOquit.

Alcohol – electrochemical sensors are affected by alcohol in high concentrations therefore cleaning wipes or hand gels containing alcohol cannot be used to clean the monitors. Alcohol can permanently damage the CO sensor but usually the sensor will recover from being saturated by alcohol after 24-48 hours left in an alcohol free environment.

Atmospheric CO – after all the above aspects have been considered, atmospheric CO should be investigated. Vast amounts of CO are released into the atmosphere by burning fossil fuels (forest fires, car exhaust emissions, and burning natural gas). People may be chronically exposed to CO as a result of smoking or from the atmosphere(2).

CO Poisoning


1. Blumenthal I. Carbon monoxide poisoning [Internet]. PubMed Central (PMC). 2017 [cited 23 April 2021]. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1281520/

2. Wright, J., 2020. Chronic And Occult Carbon Monoxide Poisoning: We Don’t Know What We’re Missing.

If the problem persists or has not been resolved by the information provided above, please contact Bedfont or your local distributor for more advice.