# Risk Factors for Distortion Product Otoacoustic Emissions in Young Adults
## 1 Introduction  
There is an increase in the research involving young adults, their use of personal music (PM) systems with earphones, and the possible effects on the auditory system. Exposure to recreational noise has risen significantly because of the high percentage of young, college-aged adults (between 90-95%) who report using digital PM systems [1, 2]. Listening habits of young adults, using questionnaire data has been obtained [1, 2, 3, 4, 5]. Specifically, [PERSON] [3] reported fewer than 50% of young adults listened to a PM system up to one hour for a single session and others have found 70-75% of young adults reported single listening sessions of one hour [2, 4]. [PERSON] et al. [5] did find that young adults reported, on average, over 14 h a week of listening to a PM system with earphones. PM system use with earphones is a recreational noise exposure that is an intermittent and variable exposure unlike occupational noise exposure; however, the level at which this use occurs is also a critical component. Researchers have been objectively evaluating the preferred listening levels of young adults using probe microphone measures [1, 6, 7, 8, 9, 10], although few have adjusted these measures for a closed canal and diffuse or free field equivalent [7, 9, 10]. The researchers that did these conversions all reported that preferred listening level was approximately 70 dBA, although all were measured in the presence of a quiet background. These preferred listening levels, however, are considered well below those that would be defined as hazardous, albeit from an occupational noise exposure perspective [11, 12]. [PERSON] and [PERSON] [10] collected preferred listening level data within a sound-treated room in an auditory research lab space. Participants were allowed to change musical tracks or adjust the volume, but this setting is not a place young adults would likely listen to music for an hour. Allowing the participants to change tracks and volume during the hour was to replicate a real-world listening condition, but when using a PM system, there is some type of background noise present, especially on a university campus. In these types of listening environments, young adults will turn the level up [7; 9]. In fact, 25% (39 of 155) of university students reported having a lot of trouble hearing people or cannot hear people while wearing a PM system with earphones [10]. [PERSON] and [PERSON] [10] further evaluated how well young adults assessed their PM system use by comparing answers to volume-specific questions to measured levels using a probe microphone. Almost 90% of young adults who reported loud or very loud volume with a PM system, listened at >85 dBA; and 83% of those that reported have a lot of trouble hearing people or cannot hear people while using a PM system listened at >85 dBA. These data show that questionnaires can be used to identify potentially risky listening behaviors in young adults. Thus, young college-aged, adults are very likely to be using PM systems with earphones, although they might not be listening at hazardous levels, and subjectively, they can rate their volume habits accurately. The effects of these listening habits on distortion product otoacoustic emissions (DPOAEs) has been mixed. Some researchers have shown an effect of PM system use on distortion product otoacoustic emissions (DPOAEs) [13] whereas others have not [14; 15], even in the presence of normal hearing sensitivity. Because some young adults do not demonstrate preferred listening levels with a PM system that might be considered at risk, are these young adults involved in other risk exposures that might contribute to subclinical damage to the cochlea (i.e., DPOAEs)? In other words, do college-aged young adults participate in activities where there is a likelihood of extensive background noise that can affect DPOAEs? One behavior of young adults linked to extensive background noise is the consumption of alcohol; particularly the consumption of alcohol in bar environments.