Hi.. Thanks for the query.. Bad smell in mouth and bad taste can be due to a number of causes like poor oral hygiene, oral and dental infections,post nasal drip, sinusitis, acid reflux,respiratory infections, diabetes etc.. If you regularly eat onion and garlic in raw form then it can also be a cause for bad taste and bad smell from mouth.. So my suggestion is to consult an Oral Physician and get evaluated so that the exact cause can be narrowed down.. For now start gargling with a flavoured mouthwash twice a day.. You should chew flavored sugarfree chewing gum.. Do warm saline gargles twice a day.. Limit the intake of high aroma foods like onion and garlic.. Steam inhalation with a few drops of Eucalyptus oil in hot water can help.. Drink plenty of water and maintain a good oral hygiene.. Hope this helps.. Regards..