Bad Breath That Won’t Go Away: Causes & When to See a Dentist

The most common causes we see are:

• Eating or drinking strong-smelling or spicy foods and drinks – garlic, onions, coffee, and alcohol are the usual suspects.
• Problems with your teeth or gums, including gum disease, cavities (holes in your teeth), or an infection.
• Fasting or crash dieting, which changes the chemicals your body produces and can affect breath.
• A dry mouth, whether from mouth breathing, certain medications, dehydration, or simply the natural drop in saliva flow overnight.
• Other medical conditions, such as tonsillitis or acid reflux.
• Smoking, which affects breath directly and also increases your risk of gum disease.

The overwhelming majority of cases – around 85-90% – originate in the mouth itself, and the single biggest contributor is bacteria coating the back of the tongue.

That area is naturally dry, hard to clean, and a comfortable home for the bacteria that break down leftover proteins and dead cells into the sulphur compounds responsible for the smell.

Far less commonly, the odour originates in the nose, sinuses, or tonsils, and genuine digestive causes are rarer still, despite being the explanation most people jump to.

Saliva is a big part of why bad breath fluctuates through the day.

It has natural antibacterial properties and physically washes bacteria off the teeth and tongue, so breath is almost always at its worst when saliva flow is lowest – first thing in the morning, during a long gap without food or drink, or in anyone with a persistently dry mouth.