Affective, or mood, disorders are often comorbidities of tinnitus. The International Classification of Diseases (ICD-10, version 2016) classifies affective disorders under mental and behavioral disorders in ICD-10 (Chap. 5). They include disorders in which the fundamental problem is a change in affect. The main types of affective disorders are depression (with or without anxiety) and bipolar disorder. Depression, or major depressive disorder, is characterized by feelings of extreme sadness and hopelessness, reduced energy, and decrease in activity, lasting at least 2 weeks. One hallmark symptom of depression, which distinguishes it from anxiety, is rumination of the past. Depression has been identified for over 20 years as a comorbidity of tinnitus (Halford and Anderson 1991) and continues to be an important research topic nowadays (Langguth et al. 2011; Weidt et al. 2016). Numerous studies have reported significant and rather strong correlations between questionnaires assessing depressive symptoms and those assessing tinnitus distress or handicap (Kehrle et al. 2016; Oishi et al. 2011). One criticism that has been raised about this association is that depression and tinnitus are usually assessed by self-report questionnaires. This method and the fact that some questions overlap in their content might artificially inflate correlations (Ooms et al. 2011). However, it is likely that this overlap may be the direct consequence of the symptomatic similarity of stressful tinnitus and depression and the fact that tinnitus questionnaires were developed to reliably reflect complaints of tinnitus patients (Langguth et al. 2011). In addition, cognitive styles have been reported as different between patients with depression and patients with tinnitus (Andersson et al. 2013), suggesting that tinnitus and depression have some degree of overlap but are not quite the same psychopathology. Nevertheless, there are longitudinal data suggesting that tinnitus-related distress decreases when depressive symptoms decrease (Hebert et al. 2012b).

Yet, evidence regarding the effectiveness of antidepressants on tinnitus (e.g., tricyclic antidepressants, selective serotonin reuptake inhibitor) is conflicting (Baldo et al. 2012; Chang and Wu 2012; Oishi et al. 2010; Robinson et al. 2005). Differences from one study to another in selection criteria (e.g., patient selection, assessment of depression and tinnitus-related distress, presence or absence of clinical depression), treatment administration (e.g., dosage), and study design (e.g., presence of control groups) all contribute to low quality of evidence.

To date, the highest level of evidence for the improvement of mood (i.e., depression and anxiety) and decrease of tinnitus-related distress is the cognitive behavioral therapy (Cima et al. 2012; Maes et al. 2014; Martinez-Devesa et al. 2010), which was originally designed to treat depression and which focuses on the development of personal coping strategies to change unhelpful patterns in cognition, behaviors, and emotional regulation.

Anxiety disorders are classified under mental and behavioral disorders in ICD-10 (Chap. 5), section “Neurotic, Stress-Related and Somatoform Disorders.” They include generalized anxiety disorder, a specific phobia, social anxiety disorder, separation anxiety disorder, agoraphobia, and panic disorder. The ICD-10 defines generalized anxiety disorder as an “anxiety that is generalized and persistent but not restricted to, or even strongly predominating in, any particular environmental circumstances (i.e., it is “free-floating”)”. The disorder is characterized by several dominant symptoms such as complaints of persistent nervousness, worry, trembling, muscular tension, dizziness, sweating, epigastric discomfort, and fear that an accident or illness will shortly happen for the patients themselves or a relative. Contrary to fear, which provokes a—normal—physiological reaction in response to a real danger, anxiety provokes a similar physiological reaction but without the danger being present. Other types of anxiety are a variation around this definition. High levels of anxiety disorders have been reported in tinnitus patients in many studies (see Sect. 3.6 below), such that anxiety is a comorbidity often found in tinnitus patients.

Personality is the combination of characteristics that distinguish an individual from all others. It determines thinking, beliefs, and attitudes and has a significant impact on health and diseases. There are several instruments to assess personality traits, usually validated and structured questionnaires. Many studies have shown that some personality traits are associated with tinnitus severity (Bayar et al. 2002; Collet et al. 1990; House 1981; Langenbach et al. 2005; Tyler et al. 2006; Welch and Dawes 2008). In particular, type D personality has been found prevalent among the tinnitus population (Bartels et al. 2010a, b). Type D personality (where D stands for distressed) describes individuals with a wide range of negative feelings and social inhibition. Type D personality overlaps the neuroticism trait, which involves a broad range of negative personality characteristics due to distress, anxiety, and behavioral cognitive impairment.

Neuroticism has also been often associated with tinnitus (Adami Dehkordi et al. 2015); therefore, neuroticism and type D personality, in particular, are associated with having tinnitus and might contribute to its perceived severity. On a more positive side, one study involving almost 5000 individuals with tinnitus indicates that tinnitus-related distress is negatively correlated with resilience and that this relationship is mediated by emotional health (Langguth et al. 2007; Wallhausser-Franke et al. 2014). This means that high resilience is associated with better emotional health or less depression, anxiety, and somatic symptom severity, which in turn is associated with a less distressing tinnitus. Working on emotional health has therefore the potential of decreasing tinnitus-related distress.

Although individual characteristics such as mood and personality contribute to tinnitus distress, other health and life conditions such as hearing and stress are important, too. Population studies with proper response rates focusing on stress and hearing are fairly recent. Even though these studies have all used self-reported measures, they are important because they minimize selection bias compared to clinical studies (Draugalis and Plaza 2009). The Swedish Longitudinal Occupational Survey of Health (hereafter the SLOSH study) (Hasson et al. 2011), which involved nearly 10,000 individuals, assessed hearing problems (including tinnitus) along with work-related stressors, long-term illness, and several other health variables. Hearing problems were classified into the three categories “no hearing problems,” “either tinnitus or hearing loss,” or “both tinnitus and hearing loss.” Unsurprisingly, the prevalence of hearing problems increased with age: in the age group comprising subjects who were 40 years old or younger, 76% reported no hearing problems, 22% reported either tinnitus or hearing loss, and 2% reported both tinnitus and hearing loss. In the age group comprising individuals 60 years old or older, only 58% reported no hearing problems, 30% reported either tinnitus or hearing loss, and 11% reported both tinnitus and hearing loss. Since hearing problems are known to be underreported, especially by older adults (Demeester et al. 2012; Kirk et al. 2012), these figures may underestimate the prevalence of hearing problems. More importantly, however, hearing problems were more prevalent in those who were exposed to work-related stressors (i.e., risk of being moved to another work/job against one’s will) or threats (i.e., threats of getting fired) than those who were not. In addition, almost-linear associations were reported across age groups between increased hearing problems and poor self-rated health, worse sleep quality, higher burnout, and greater long-lasting stress, that is, as health, sleep quality, burnout, and long-lasting stress levels got worse, the more hearing problems were reported as well.

In a subsample of the SLOSH study where the focus was more specifically put on tinnitus, hearing loss, uncomfortable loudness levels, and emotional exhaustion (i.e., long-term stress) were significant predictors of tinnitus prevalence (Hebert et al. 2012a). Interestingly, among individuals with tinnitus, emotional exhaustion was highly correlated with tinnitus severity (as assessed by the Tinnitus Handicap Questionnaire) when factoring out hearing loss, whereas hearing loss was not correlated with tinnitus severity when factoring out emotional exhaustion. In other words, the relationship between hearing loss and tinnitus severity was fully explained by long-term stress.

The influence of stress and noise exposure on the probability of having tinnitus was examined in a parallel study. In a population sample of 12,166 adults aged from 18 to 84 years old (Baigi et al. 2011), the prevalence of tinnitus was 16.6%. Overall stress (i.e., a “yes” answer to the question “Do you feel stressed at present?”) was almost as important as noise exposure for the severity of tinnitus, and among those who had tinnitus, increases in stress levels were more important than noise exposure for the transition from mild to severe tinnitus. In other words, current stress self-reported levels were a more determining factor for severe tinnitus than noise exposure. The probability of having tinnitus was twofold when exposed to both noise and stress, with respect to when exposed to either noise or stress.

Some smaller studies corroborated and expanded these findings by focusing on the prevalence of tinnitus among more specific samples of workers exposed to work-related stress. One study conducted in 250 musicians coming from 12 symphony orchestras (Hasson et al. 2009), epidemiological study reported a prevalence of 42% for hearing problems (i.e., a “yes” answer to the question “Do you have any hearing problems?”). Hearing problems (including, but not limited to, tinnitus) were strongly associated with medical symptoms (e.g., headache, muscle pain), stress-related symptoms (e.g., physical or mental fatigue, worry), and work satisfaction (e.g., frustration at work due to bad conductor). Thus, once again stress—either work related or not—was associated with hearing problems. Similarly, high tinnitus prevalence was found in a study involving 1100 operators (79% women) in call centers of two large communication companies (Lin et al. 2009). Overall prevalence of tinnitus was 40.3% and significantly higher in women (48.3%) compared to men (32.3%). In addition, operators of both genders with higher job stress (i.e., those who responded “always” or “often” to the question “How frequently do you feel stressed at work?”) had more than twice the risk of various health complaints, including tinnitus, compared to low-stress operators. Although none of the two above studies assessed the influence of environmental noise on hearing or tinnitus, one can assume that both symphony orchestra musicians and call operators work in noisy environments and that the very high prevalence rates of tinnitus might reflect a combined effect of noise exposure and stress.

Finally, a recent study conducted in 1632 employees of a large pharmaceutical company investigated more precisely the impact of work-related stress on tinnitus, controlling for many factors including noise exposure. Work stress was conceptualized in terms of organizational justice, which is perceived fairness at the workplace (Stattrop et al. 2013). Overall organizational justice was inversely related to tinnitus, that is, the lower the perceived justice, the more frequent the tinnitus was reported. Although this association was independent of demographics, socioeconomic status, job characteristics—including potential noise exposure—and health behaviors, it was partly explained by individual differences in depressive symptoms and, more particularly, in burnout symptoms. In other words, burnout, which pertains exclusively to the work context, is the underlying mechanism by which the lack of fairness at work is associated with tinnitus prevalence.

In sum, if the role of noise exposure as a risk factor for tinnitus prevalence has been known for a long time (Mazurek et al. 2010), data is now accumulating about psychological factors such as chronic and work stress as even more important factors than noise exposure for tinnitus prevalence and severity.

The direction of the relationship between tinnitus severity and stress cannot be determined from these studies, i.e., whether severe tinnitus causes stress or whether stress can trigger severe tinnitus (Figs. 3.2 and 3.3). Although the traditional view has been that tinnitus causes stress and that a main therapeutic objective is to reduce the stress caused by tinnitus (Stattrop et al. 2013), other models suggest that the other possibility is equally plausible (Rauschecker et al. 2010).

Let us consider the first possibility, that is, that severe tinnitus causes stress: The sound is perceived as an alarm signal that creates an emotional stress, which activates the hypothalamic-pituitary-adrenal (HPA) axis (see Chap. 2) and sympathetic nervous system (SNS) (Mazurek et al. 2015). At first, basal cortisol levels may increase and because of the chronic stress could be followed by an enhanced sensitivity to negative feedback, eventually resulting in a blunted acute stress response and HPA axis exhaustion (see (Mazurek et al. 2015) for a more detailed description of the model). Indeed, clinical studies using the stress hormone cortisol as an objective measure of stress have shown that tinnitus is associated with significant HPA axis dysregulation as found in other stress-related diseases (Hebert and Lupien 2007; Hebert et al. 2004; Simoens and Hebert 2012). Although compatible with the hypothesis, these studies are not longitudinal, and therefore the causality of the relationship cannot be ascertained.

A different model proposed a relationship in the opposite direction between emotional factors and tinnitus (Rauschecker et al. 2010). This model assumes the widely accepted idea that the initial tinnitus signal results from peripheral deafferentation and subsequent lesion-induced cortical plasticity. According to this model, limbic and auditory brain areas interact at the thalamic level. The tinnitus signal can be tuned out by feedback connections from limbic regions, which block the tinnitus signal at the thalamic level from reaching auditory cortex (compensated tinnitus). If the limbic regions are dysfunctional, for instance, by way of chronic stress, sleep deprivation, or depression, this noise-cancellation mechanism breaks down, resulting in chronic tinnitus. The model is interesting because it explains that hearing loss can occur without tinnitus. However, the model does not make predictions about the severity of tinnitus: tinnitus is either present or absent.

A further interesting model, although not proposed for tinnitus specifically, is the one of O’Donovan and colleagues (O’Donovan et al. 2013). According to this model, and coming back to individual traits, anxious individuals have an exaggerated neurobiological sensitivity to threat that may lead to sustained threat perception. This threat perception, expressed by cognitive biases in threat-related information processing, is accompanied by prolonged activation of threat-related and threat-responsive biological systems such as the HPA axis, autonomic nervous system (ANS), and inflammatory response. This pattern of responding can over time produce chronic inflammation through structural and functional brain changes, dysregulation of the HPA axis and ANS, and accelerated cellular aging. Thus, individuals with chronically high levels of anxiety are at increased risk for several aging diseases such as cardiovascular, autoimmune, and neurodegenerative disorders. If applying the model to tinnitus, it is possible that in anxious individuals who are in a chronic state of cognitive-behavioral avoidance of perceived threats, i.e., constantly scanning their environment for possible threats, will perceive tinnitus as a major threat to their health when it happens and judge it as very disturbing (see Fig. 3.4). This vulnerability will activate or renew—because it has been already activated through past experiences of environment or personal events—threat-related and threat-responsive biological systems such as the HPA axis, autonomic nervous system (ANS), and inflammatory response. In other words, it is likely that anxious individuals have already shown signs of advanced deleterious bodily responses, well before tinnitus appears, such as a dysregulated stress response, and thus tinnitus will only keep this maladaptive physiological response going. Therefore, it is not surprising that a high percentage of tinnitus patients have a lifetime history of depression and anxiety and that only a small percentage report that they had tinnitus prior to their disorder (Zöger et al. 2001). Also not surprising is the fact that emotional exhaustion, which supposedly takes time to develop, is a more important factor compared to hearing loss for tinnitus severity (Hebert et al. 2012a).