"People move away when I speak. At meetings, I see colleagues leaning back in their chairs or actually covering their noses. I brush my ... teeth every day, but the smell is unbearable."
Xurxo went to see dentist Simón Pardiñas because he was obsessed with the unpleasant odour coming from his mouth. He no longer knew how to resolve the situation, even though in his specific case, the smell was far less severe than he believed.
"Bad breath isn't just a much more common problem than we realise; it's also a source of stigma for those who suffer from it: it causes a great deal of rejection and low self-esteem," said Pardiñas, author of Cuida tu boca (Care for Your Mouth) and associate professor in the Department of Oral and Maxillofacial Surgery at New York University.
"They're even too embarrassed to seek advice. Xurxo, for example, became traumatised by a smell that wasn't actually that strong because one day someone made an unfortunate comment to him."
In most cases, bad breath originates inside the oral cavity, primarily due to poor oral hygiene. Rather than being a distinct disease, the unpleasant odour serves as a symptom that an underlying issue requires attention.
"Just as with body odour, halitosis is caused by hundreds of volatile compounds produced mainly by bacteria that colonise the oral cavity," explained Raúl Rivas, Professor of Microbiology at the University of Salamanca. "These microorganisms can break down everything from sulphur-containing amino acids to compounds such as hydrogen sulphide, which has that characteristic smell of rotten eggs.
Other examples of malodorous microorganisms include the bacterium Proteus mirabilis, which smells of fish, and Eikenella corrodens, which gives off an odour similar to that of bleach."
While the majority of cases stem from the mouth - originating on the posterior third of the tongue, inflamed gums, tooth decay, partially erupted wisdom teeth, or tonsilloliths (tonsil stones) - causes can occasionally lie outside the oral cavity, including sinusitis, rhinitis, hiatal hernia, poorly controlled diabetes or digestive issues.
Pathological vs physiological causes
Dental specialists divide halitosis into two distinct categories: pathological and physiological.
Pathological halitosis stems from underlying medical conditions, such as periodontal diseases like gingivitis or periodontitis, issues with the parotid glands, or dry mouth (xerostomia). "In the long run, a neglected mouth leads to the build-up of plaque and tooth decay, as well as contributing to the accumulation and putrefaction of food debris, which promotes microbial breakdown and, consequently, bad breath," Pardiñas noted.
Physiological halitosis, by contrast, is linked to temporary or lifestyle factors rather than underlying disease. Morning breath occurs when salivary flow naturally decreases overnight, though it is easily resolved with morning brushing.Ageing also contributes to a drier mouth environment as saliva production diminishes over time.
Dietary habits play a significant role as well; highly restrictive or low-carbohydrate diets push the body into ketosis, releasing a distinct acetone-like odour on the breath, while fasting reduces the saliva needed to wash away organic debris.
Meanwhile, tobacco smoke leaves persistent chemical residues, alcohol dehydrates oral tissues to suppress saliva production and removable appliances like dentures or aligners require dedicated cleaning to stop bacterial accumulation.
Despite these varied causes, specialists stress that bad breath improves significantly or disappears entirely once a rigorous, targeted oral hygiene routine is established.
Dentists recommend brushing teeth after every meal, using dental floss or interdental brushes for gaps, and scraping the tongue from back to front using a dedicated tongue cleaner or toothbrush. A light brush over the inner cheeks and roof of the mouth helps break up microbial biofilms on mucous membranes.
Regarding mouthwashes, specialists advise caution. While chlorhexidine rinses can help in early treatment phases or following deep dental cleans, prolonged use should be avoided as it can stain teeth and alter taste perception. Mouthwash should never replace physical brushing.
For removable dentures, aligners or mouthguards, experts advise removing them at night, rinsing them with cold water, and soaking them in effervescent cleaning solutions every two weeks. Hot water and abrasive toothpastes should be avoided to prevent surface damage that traps bacteria.
Dietary adjustments also play a central role. Reducing heavy or meat-heavy evening meals, avoiding long periods of fasting, limiting alcohol and quitting smoking remain essential steps. Foods rich in sulphur compounds, such as garlic and onions, enter the bloodstream during digestion and continue to be exhaled through the lungs for hours afterwards.