Over at Ask Metafilter, Srudolph asks:My son and his dad (my former husband) never have bad breath. How is this possible?
Halitosis is mostly caused by microorganisms breaking down the food particles left in our mouths. Right, now, we know that people can have fairly different microbial populations, but don’t have a good handle on why that is. Some of it is certainly environmental, related to eating habits and such, but some of it also depends on personal factors. The immune system plays a role in culling these bacteria, and there are probably other contributors, like slight differences in the pH of your saliva, that might make all the difference.
Factors like these last two may be partially genetic, which explains why your husband and son have similarly fresh breath. Since we don’t yet know enough about these dynamic microbial ecosystems to control them, your best bet is to brush after meals, and be glad that you don’t have to kiss a smelly spouse.
If you’re interested in learning more about the trillions of microorganisms that inhabit your body, read up on the Human Microbiome Project, which is trying to characterize and understand them.