Previous researches have already established that second-hand smoke causes similar harms as direct smoking including lung cancer, ear infections, heart diseases, respiratory prblems, and cognitive impairment.
Experts believe that smoking disrupts the blood flow in ear vessels. This leads to deficiency of oxygen in the organ, which further results in accumulation of toxic waste, causing the impairment.
Reportedly, second hand smoke (SHS) is known to produce more particulate-matter (PM) pollution compared to an idling low-emission diesel engine.
In a bid to find the possible link between passive smoking and risk of hearing loss, lead researcher Dr. David Fabry from University of Miami studied 3307 non-smokers, aged 20-69, some of whom were former smokers and others who had never smoked in their lifetime.
Researchers assessed the degree of hearing loss in volunteers by testing the range of hearing from over 500 Hz (low) to 8000 Hz (high).
Also, the study authors took blood samples of these volunteers to measure the amount of byproduct of nicotine, called cotinine, made in the body when it comes in contact with tobacco smoke.
Dr. Fabry said, "We really do not know exactly how much smoke you need to be exposed to in order to be at increased risk. But we do know that the threshold for damage is very low.
"Really, the safe level of exposure is no exposure."
The study found that both direct and passive smokers were exposed to hearing impairment, the risk being higher in former smokers than in non-smokers.
Furthermore, it was found that men aged above 50 and those with diabetes were more susceptible to high-frequency hearing loss.
Though the risk was less pronounced in non-smokers, around nine percent were at low- to mid-frequency hearing loss risk and 27 percent were exposed to high-frequency hearing loss.
Dr. Ralph Holme, head of biomedical research at the RNID (Royal National Institute for Deaf People), said, "We already knew from our own research that regular active smoking is a significant risk factor leading to hearing loss and this new study is important as it highlights the increased risks posed by passive smoking too.
"Hearing loss can often be very frustrating and lead to social isolation, if not quickly addressed. Before you next light up a cigarette, consider how it could impact not only on your own long-term hearing but your friends' and relatives' too."
Findings of the study appear online in the journal 'Tobacco Control'.