Modern life is enveloped in scents, from aromatic candles to car air fresheners to old books. But a surprising number of people are plagued by being able to smell odors that don’t really exist. The inescapable whiff of smoke, rotten eggs, or other unpleasant stenches can be a debilitating experience, and now science is beginning to have an idea of just how common it is.

A new study published in JAMA Otolaryngology-Head and Neck Surgery this week and led by the National Institute on Deafness and Other Communication Disorders (NIDCD) looked at the phenomenon of "phantom" odors that have no obvious source. Data collected between 2011 and 2014 was taken from the National Health and Nutrition Examination Survey, with 7417 subjects aged 40 and over detailing their perception of phantom smells. Respondents were asked if they smelled an unpleasant, bad, or burning odor regardless of their location. Of the 7417 people polled, 534, or about 6.5 percent, reported sensing persistent smells undetected by anyone else in the vicinity.

Researchers also found a correlation between people detecting phantom smells and quality of life. Those who reported unexplained odors expressed an overall dissatisfaction with their mood and had trouble maintaining their weight. Twice as many women as men indicated they had a problem with such odors, though researchers aren't sure why.

The study also found a correlation between reports of this problem and a history of head injury, dry mouth, and overall poor health. It's possible medications used to treat chronic conditions, or environmental pollutants, could be factors, but more research needs to be done to make specific determinations.