Of course it is not usual for a young child to have bad breath. You have excluded dental decay as a possible cause by seeing your dentist. The most common cause of bad breath at this age is simply due to chronic mouth breathing especially when sleeping. The main cause of mouth breathing is a persistently blocked nose. If you suspect that your son has a blocked nose then he should be seen by an ENT specialist. Other causes of bad breath include sinus infection, tonsil infection or sometimes something that the child has pushed up the nose such as a peanut or small bead. This usually occurs in younger children than your son's age group.In any case it may be a good idea to see an ENT specialist as all of thes possible causes need to be excluded.
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