What bloodborne body odor and halitosis means

According to the Merriam-Webster’s Online Dictionary, borne means “to transport or transmit by - used in combination 'soilborne' 'airborne" [1], and the Merriam-Webster’s Medical Dictionary defines blood-borne as “carried or transmitted by the blood”. [2] This could be anything from blood-borne nutrients, blood-borne hormones, a blood-borne disease, etc. Although serious contagious diseases can be blood-borne, most everything that is blood-borne is not a contagious pathogen, and most people don’t have blood-borne contagious pathogens.

Most certainly, metabolic bloodborne body odor/halitosis has nothing to do with contagious/bloodborne pathogens. When we refer to bloodborne body odor, we refer to the abnormal levels of odorous chemicals allowed (mainly) by the liver to enter the main circulation, and the subsequent toxins this imbalance produces that are carried in the main circulating blood and excreted unchanged through the body’s cleansing organs, such as the kidneys, skin, breath (via the lungs), etc. This results in body odor and/or halitosis that stems from the internal system.

The odorous chemicals present in the bloodstream can be the product of a low amount of the metabolic enzyme(s) that otherwise would normally neutralize the odorous chemicals before entering the bloodstream (or in some cases, chemicals produced internally e.g. hormones). Another cause could be simply because the enzyme(s) is completely overloaded (saturated) by the load it has to deal with. For instance if you eat garlic and smell, this is the garlic chemicals overloading an enzyme(s) that is supposed to neutralize the chemicals before they enter the main circulation. And of course, it could also be caused by both.

This concept is mentioned by Dr. Stephen Mitchell, Biological Chemistry, Biomedical Sciences, Faculty of Medicine, Imperial College London, in his article, SC Mitchell (2005) Trimethylaminuria (fish-odour syndrome) and oral malodour, in which he states,

A small but important percentage of oral malodour cases have an extra-oral aetiology and certain of these fall into the category of ‘blood-borne halitosis’. Odoriferous substances generated within the body and transported to the lungs via the circulatory system may, if sufficiently volatile, leave with the exhaled air and impart a foetid odour to the breath. [3]

References:
1. http://www.merriam-webster.com/dictionary
2. http://medical.merriam-webster.com/medical/blood-borne
3. http://www.blackwell-synergy.com/doi/abs/10.1111/j.1601-0825.2005.01081.x