Hello, There are 3 reasons for bad smell in mouth-- 1.Dental caries or poor oral hygiene 2. acid reflux from stomach ie acidity or heart burn , in addition constipation. 3. Nasal disease- due to nasal discharge which trickles down there can be such smell. Treatment------- 1.Dental caries or poor oral hygiene---dental doctor opinion , brush mouth 2 times a day. avoid smoking or alcohol 2.acid reflux------- Antacid tablet like proton pump inhibitors with domperidom Syp. antacid gel 2 tsf two times a day half an hour before meals multivitamin twice daily Keep head end of bed elevated. Avoid alcohol, Smoking Do brisk walking daily Go for walk after dinner Avoid spicy food Avoid late night coffee 3.Nasal disease--- Get ENT opinion,, examination of nose can be done and if there is any disease then CT scan can be done to see for disease, then further management can be planned.