Oral halitosis (90% of cases)
It originates in the oral cavity itself. In 41% of oral halitosis cases, it is primarily due to the accumulation of oral biofilm (bacterial plaque) on the tongue. Other contributing factors can include periodontal problems, dental caries, and smoking habits, among others.
Extraoral halitosis (10% of cases)
It originates outside the oral cavity. It is mainly due to systemic disorders affecting the upper/lower respiratory tract or the digestive system and to liver or kidney diseases.

In general, it is unlikely for one to notice their own bad breath, so halitosis is difficult to diagnose. However, a dental professional can assist in identifying the issue.

Non-pathological
Morning breath: during sleep, saliva flow decreases, allowing bacteria to proliferate and produce foul-smelling gases.
Age: older adults may experience regressive changes in their salivary glands, affecting the quality and quantity of saliva, even with good oral hygiene.
Dental prostheses: ldentures and bridges can trap food debris, leading to bad breath.
Medications: certain medications, such as anticholinergics and antidepressants, can cause xerostomia (dry mouth). Saliva plays a crucial role in cleaning the oral cavity and reducing odours.
Tobacco: smoking can create a distinctive breath odour that may persist for several days, even after quitting.
Fasting periods
Diet: consuming certain foods (onions, garlic) or alcohol.
Pathological
Periodontal disease, caries.
**Poor oral hygiene:**nadequate removal of bacterial plaque leads to bacterial growth. The places where bacteria usually accumulate are the tongue, in interproximal spaces, the subgingival area, and around abscesses.
Ulcerative causes: traumatic ulcers, infectious ulcers, stomatitis.
Pharyngeal Infections viral, bacterial or fungal.
Necrosis due to radiation therapy and chemotherapy in patients with neoplasms.
The possible causes of extraoral halitosis include: conditions such as nasal issues (sinusitis), digestive diseases, respiratory diseases, systemic diseases (poorly controlled diabetes mellitus, kidney infections, liver dysfunction, Sjögren's syndrome, rheumatoid arthritis, etc.).

Halitosis can significantly impact the quality of one’s personal life, diminishing their self-confidence and complicating their interpersonal, intimate, and professional relationships, as it interferes with verbal communication and potentially leads to social rejection.
Moreover, it is associated with a person’s general health status, lifestyle, oral condition, and hygiene habits.
Beyond being an aesthetic issue, the implications of bad breath can be directly linked to more serious problems, such as cavities, gingivitis or periodontitis.