Most of us face a problem of bad breath in the morning when we wake up. Bad breath is also called as halitosis which affects half of the adults at one time or another as per American Dental Association.

Scientists have been reviewing the condition in order to bring a solution to it. They have been reviewing whether probiotics can be useful halitosis treatment.

Dr. Matt Messina, a consumer advisor for the American Dental Association and assistant professor at the college of dentistry at The Ohio State University, told Healthline, “The whole idea behind probiotics is if we have a group of bacteria in the environment that we don’t like if we introduce bacteria that we do like and can supplant the ‘bad guys’ with the ‘good guys,’ then we’ll end up with a better result.” 

Foods that contains probiotic bacteria would include yogurt and sourdough bread. There are some probiotic supplements in the market, although the benefits of swallowing a capsule might differ from when chewing the probiotic foods.

“[The research] is very thought-provoking. The value is that it pulls a lot of studies together to show where the gaps in the research are. And the gap here we really need to go after is causality,” Messina added.

There are some people with halitosis who did experience a short term improvement, it's not yet clear is it is the reason.

Sources: https://www.healthline.com/health-news/bad-breath-how-fermented-foods-such-as-yogurt-can-help-prevent-halitosis#Treating-halitosis