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Hello this is Dr. Salama MD,
Foul smelling breath is typically caused by some sort of bacteria.
The 3 most common locations for bacteria causing foul breath are the tongue, teeth or lungs.
In this age, it's likely the teeth since they have a hard time flossing and occasionally brushing regularly.
If it was his lungs, he would have had pulmonary issues by now such as shortness of breath, cough or frequent lung infections.
I would advise you to take him to the dentist for a thorough cleaning and to teach him how to properly floss.
Let me know if you have any other questions.
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