Smell receptors in the body could help diagnose and treat diseases such as cancer, a review of over 200 studies has found.
The study, published in the journal Physiological Reviews, shows that olfactory receptors - proteins that bind to odours that aid the sense of smell - perform a wide range of mostly unknown functions outside the nose.
The function of extra-nasal olfactory receptors has the potential to be used in the diagnosis and treatment of health conditions such as cancer, said researchers from the Ruhr-University Bochum in Germany.
Olfactory, or smell, receptors were originally thought to be only in the sensory nerve cells (neurons) of nasal cavity tissues.
However, more recent and extensive study suggests that the receptors "occur in nearly the entire human body, and they appear to be substantially more functionally important than previously suggested," the researchers said.
In addition to the receptors playing a major role in the sense of smell, "several essential physiological and pathophysiological processes have been described as targeted by human (olfactory receptors), including path finding, cell growth, (cell death), migration and secretion," they said.
The existence of olfactory receptors outside the nose - either positive or negative - plays an important role in disease progression and physiological function but is not yet fully understood, the researchers said.
The review revealed ways in which olfactory receptors may affect the development of disease.
The researchers said that the receptors concentrated in the prostate tissue, especially in men with prostate cancer, contribute to the reduction or progression of the disease.
Receptors in the colon may reduce the growth of colon cancer cells, they said, while receptors in the digestive tract may cause chronic diarrhea or constipation but may also contribute to better digestion.
