Yawning is an involuntary social behavior that occurs spontaneously and contagiously [1]. Spontaneous yawning is present in humans from the fetal period and continues until the end of life [2]. In childhood, its cases are relatively high and it decreases a little with aging [3]. Yawning is a complex action that is controlled by the hypothalamus and brainstem, especially the paraventricular nucleus, and several neurological factors such as serotonin, dopamine, and oxytocin are effective in its induction [4]. Yawning is a cascading respiratory cycle that occurs within 5–10 seconds, with the contraction of different muscles, the mouth opens and the airway tube expands, so that the diameter of the pharynx increases 3–4 times and a long inhalation takes place. It is followed by breathing and short exhalation [5]. Yawning tasks are probably circadian sleep-wake rhythms [3], arousal modulation [6], regulation of vigilance, group synchronization [1], brain cooling [7], and long-term oxygenation [5].

Yawning is a symptom of physiological and pathological behaviors. If yawning is repeated more than three times in 15 minutes, it is considered as pathological yawning [4]. Pathological yawning has various causes, and one of the most important of them is the use of some psychotropic drugs such as paroxetine, sertraline, and especially fluoxetine hydrochloride [8]. Some diseases such as migraine, epilepsy, and multiple sclerosis (MS) increase the incidence of yawning [9] and in some disorders such as autism and schizophrenia, the incidence of yawning decreases [10]. In autism patients, the reduction of contagious yawning is secondary, which is to reduce attention to other people’s faces, and in these people, there is no reduction in emotional empathy, but people with psychopathic traits show lower levels of empathy [11].

Spontaneous yawning is related to the transition between sleep and wakefulness and vice versa, and dull and monotonous situations can create it [1]. But in contagious yawning, a person experiences yawning by seeing it, hearing its sound, reading or thinking about it, and can hardly control it. Contagious yawning is more common among family members and friends [12]. Despite the variability of people’s responses to yawning stimuli, a few studies have been conducted on the factors affecting people’s susceptibility to spontaneous and contagious yawning in the Middle East, so we decided to investigate the effective stimuli for causing yawning and fatigue, which caused a decline in educational quality, in northwest of Iran. In this way, we can be helpful in improving social interactions and communication, especially among students.

This study was conducted on students, faculty members and staff of Tabriz University of Medical Sciences and Tabriz University with the approval of Tabriz University of Medical Sciences Ethics Committee (IR.TBZMED.REC.1402.124). A questionnaire in May or September 2023 including age, sex, height, weight, occupation, faculty and field of study, place of yawning in terms of temperature, time of yawning, amount of yawning, sleep conditions, creation modes and the occurrence of yawning while filling the questionnaire and the level of stress in life were filled by the volunteers. People with possible confounding diseases such as epilepsy, MS, schizophrenia, and psychotropic drug users were excluded from the study and finally 250 volunteers (84 males & 166 females) were selected.

The subjects studied were 19–60 years old (average 23.18). One hundred and ninety-eight people (79.2%) yawn while seeing another person yawns, 173 people (69.2%) in fatigue, 165 people (66.0%) in a long and boring lecture, 152 people (60.8%) in insomnia, 150 people (60.0%) in classroom, and 114 people (45.6%) yawned more when they heard the sound of yawning than in other situations (Table 1). Sixty-one point two percent of the studied subjects yawned in a hot place, 11.2% in a moderate place, and 27.6% in a cold place. Seventy-four people (29.6%) yawned more at 8–10 AM, 46 (18.4%) at 2–4 PM, and 39 people (15.6%) at 10–12 PM. One hundred and fifty-seven people (62.8%) felt yawning while filling the questionnaire.

Yawning occurs as a result of internal and external stimuli that can spread and with involuntary synchronization, it causes intergroup coordination and facilitates communication in social groups [13]. In this study, 54 internal and external stimuli could cause yawning in 250 healthy volunteers working in two important and large universities in the northwest of Iran. The most important cause of yawning was seeing others yawning (79.2%), which was more common among young students, especially girls, than among middle-aged people, and in the later stages it was fatigue (69.2%) and attending a long boring lecture (66.0%), but the stimuli of aggression (2.4%), fear (3.6%), stressful situation (5.2%), and hunger (10.8%) had less effect on people’s sensitivity to yawning (Table 1), which is similar to De Weck et al.’s [14] study that found contagious yawning in 71.4% of participants, but in the other two studies, visual contagious yawning was 67.7% [10] and 62.7% [15] which were in contrast with our study. The difference in the results is probably due to the fact that most of our participants were students, in which the group behavior is close to each other, and more of them live together in the dormitory, and it was their own statement that they had contagious yawning, while the two studies were done through video stimulus [10,15] and also in our study, people with psychopathic traits were excluded, in which cases of contagious yawning are reduced [10]. In addition, compared to the other two studies that were from different populations, in this study, participants were Iranian, whose different genetics can have an impact on the results. In this study, 45.6% of people had auditory yawning, which is less than 79.2% of visual yawning and is similar to the results of De Weck’s study [14]. Therefore, it seems that yawning as a social and emotional communication behavior spreads more through seeing than through hearing.

In this study, a significant number of participants were young students (average age=23.2 years), so similar to another study [16], they had more cases of yawning, but middle-aged people had fewer cases of contagious yawning. Therefore, it seems that with increasing age, people show few social interactions. Most young people lived together in a dormitory and had close relationships because contagious yawning is created with emotional closeness between people, and is more common among friends and relatives than among strangers and acquaintances [12].

Tiredness was the second cause of yawning among the participants by 69.2%. Fatigue is one of the strongest causes of yawning in young people aged 20–24 years, who made up the majority of our volunteers [15]. However, in elderly people the role of tiredness is less, and in female participants, it was about twice as much as in male participants, and similar to other studies [6,12], there were more cases of contagious yawning in females. This can indicate the possible effect of sex hormones on the frequency of yawning behavior. Yawning in highly social strains is affected by emotional contagion [13]. Moreover, adults aged 18–25 years respond even to the yawning of non-relative children aged 2–6 months [16]. Of course, in addition to individuals’ genetics, hormones such as oxytocin are also effective in the contagiousness of yawning, so that autistic people with high oxytocin in contagious yawning are no different from children who are growing normally, but if the amount of oxytocin in the blood is low, contagious yawning decreases. So, this hormone plays a role in social behavior and empathy [17] and oxytocin itself is also effective in altruism and regulates intergroup conflicts through altruism and oxytocin induces the desire and defense response, i.e., it promotes trust and cooperation within the group and defensive aggression towards rival outgroups [18]. It should be noted that contagious yawning is not equal to empathy and various variables such as social inhibitors, individual characteristics, acute physical stress, environment, age, time of day, weather conditions, and seasonal temperature changes have an effect on its frequency [19]. In the studied subjects, only one-third (1/3) of participants had proper sleep and two-thirds (2/3) did not sleep properly that most of them (36%) were late sleepers and 10.4% were insomniac and also 20.4% of people had excessive or minimal sleep or snoring during sleep.

Due to sleeping late, a significant number of them, 60%, were yawning in the classroom, which was mostly held in the morning that is caused by sleeping late, especially in the dormitories where guest students are present in the rooms, and prevent students from sleeping on time. It makes students to be sleepy in class, which causes them to yawn. In the studied subjects, the most yawning was at 8–10 AM (29.6%) because most of the participants were 20–24 years old and lived in university dormitories and slept late at night. Due to lack of sleep, they were sleepy after waking up. Sleepiness is one of the important causes of yawning [3], one of the important factors in the yawning of the study participants and the main cause of students yawning at 8–10 o’clock in the classroom. Sleepiness is caused by the late sleeping of students due to being busy in the virtual world. It seems likely that the increase in yawning cases during the day is due to sleep deprivation during the night, which causes the regulation of alertness during sleepiness [5,15]. Training and planning for students to sleep early can be useful.

According to the possible function of yawning in intergroup communication [1,13] and oxygenation [5], the change of yawning cases in different conditions of people, its influence by dopamine, serotonin [4] and its increase due to the use of some drugs [12] and the change of the number, It can be used as a clinical marker in neurobehavioral evaluations in various diseases such as MS [9].

In this study, there were the following limitations: First, the study of the frequency of contagious yawning is influenced by the seasons and ambient temperature, and it can probably not be unaffected in the study that was conducted in May and September. Secondly, yawning is influenced by the amount of sleep in the previous night. Thirdly, the circadian rhythm of the maximum number of students in the dormitory was disturbed to sleep late. It is suggested to determine the relationship between yawning and other life habits, such as eating habits, consumption of ready-made foods, the amount of stress in life and staying awake at night, genetic polymorphism, hormones that are effective in yawning, and their receptors.

From this study, it can be concluded that the most important triggers of yawning are seeing others yawning, fatigue, attending a long and boring lecture, insomnia, and being in class, and sleeping late plays an important role in causing them. According to the stimuli, it seems that yawning is probably responsible for regulating alertness during sleepiness, which facilitates communication with contagion.