People who struggle with severe internet addiction might experience long-term changes in how their bodies process stress. A recent study analyzing human hair samples found that higher levels of internet addiction symptoms are linked to lower long-term accumulations of the stress hormone cortisol. The research was published in the journal Psychoneuroendocrinology.
Internet addiction is widely recognized as a behavioral disorder involving excessive and poorly controlled online activity. This can include anything from endless social media scrolling and online gaming to excessive internet shopping. The behavior becomes an addiction when it causes marked distress or impairs a person’s ability to function in their daily life, such as failing to fulfill obligations at school or work.
Psychologists have consistently linked internet addiction to high levels of psychological stress. Some theoretical models suggest that people who are highly vulnerable to stress may use the internet as a coping mechanism to escape negative emotions. However, studies looking at the physiological side of this stress response have yielded conflicting results.
The human body manages stress through a biological network known as the hypothalamus-pituitary-adrenal axis, which ultimately produces cortisol. Cortisol is often called the primary stress hormone. In healthy amounts, it helps the body respond to immediate challenges, but chronic stress can alter how the system functions.
Previous research trying to measure cortisol in people with internet addiction has mostly relied on saliva or blood samples. These testing methods are highly sensitive to momentary fluctuations. A person’s cortisol levels can change based on the time of day, recent exercise, alcohol consumption, or a brief moment of anxiety just before the test.
To bypass these momentary spikes, scientists Hideki Tsumura of Tokushima University and Shuhei Izawa of the National Institute of Occupational Safety and Health in Japan turned to a different testing method. They chose to measure hormones trapped within human hair. Hair grows at an average rate of roughly one centimeter per month.
By analyzing a three-centimeter snippet of hair cut close to the scalp, researchers can measure the total amount of hormones secreted over the preceding three months. This provides a stable biological diary of long-term hormone production.
The researchers also decided to measure a second hormone called testosterone. Produced by a different biological network, testosterone is often associated with reward processing and risk-taking behaviors. Some neurobiological studies suggest that individuals who are prone to risk-taking might have heightened reward sensitivities driven by testosterone.
Because internet addiction often involves choosing immediate online rewards despite long-term negative consequences, the researchers suspected testosterone might play a role. The two biological systems that produce cortisol and testosterone also interact with one another. High levels of cortisol can suppress testosterone production, while testosterone can inhibit the release of cortisol.
Tsumura and Izawa wanted to examine both hormones simultaneously to see how each related to internet addiction symptoms. They recruited 155 Japanese university students for the study. The group included 94 women and 61 men, with an average age of roughly 21 years.
The researchers applied strict criteria to ensure the biological samples would be viable. They excluded individuals who had endocrine disorders, acute psychiatric conditions, or who were taking medications known to affect hormone levels, including hormonal contraceptives.
Participants completed a standardized survey known as the Internet Addiction Test. The questionnaire asks individuals to rate how often their internet use disrupts their sleep, academic performance, or social interactions. The students also completed a separate assessment to measure current depressive symptoms.
Following the surveys, the research team collected the hair samples from the back of each participant’s head. In the laboratory, they washed the hair samples in chemical solvents to remove external contaminants. The hair was then flash-frozen in liquid nitrogen and ground into a fine powder so the trapped hormones could be extracted and quantified.
To analyze the data, the researchers used statistical models that controlled for various outside factors. They adjusted the numbers to account for age, sex, body mass index, and depression scores. They also factored in hair care habits, such as bleaching, perming, and how many times a week the participants washed their hair.
The results showed that hair cortisol concentrations were negatively associated with internet addiction scores. Students who reported more severe symptoms of internet addiction had lower amounts of cortisol trapped in their hair. When the researchers divided the participants into two groups based on a standard cutoff score for internet addiction, the highly addicted group exhibited lower average cortisol levels than the low-risk group.
The initial hypothesis regarding testosterone was not supported by the data. The researchers found no association between internet addiction symptoms and long-term hair testosterone concentrations. The results remained consistent across both male and female participants.
Finding low levels of a stress hormone in people experiencing high psychological distress might seem counterintuitive. The researchers point out that chronic stress exposure can initially trigger high cortisol production, eventually leading to a state of biological exhaustion. Over time, the stress system may become blunted, resulting in lower baseline cortisol secretion.
Reduced hair cortisol levels have also been observed in people experiencing post-traumatic stress, severe depression, and prolonged adversity. The findings suggest that individuals with severe internet addiction might share a similar underlying biological profile characterized by an exhausted physiological stress response.
The authors noted a few limitations to their work. Because the study relied on a specific demographic of young university students, the findings may not represent the general population or older adults in clinical settings. The research was also cross-sectional, meaning it captured a single snapshot in time.
Without longitudinal data, researchers cannot determine the sequence of events. The data cannot show whether an altered stress system makes someone more vulnerable to internet addiction, or if the behavioral addiction eventually causes the stress system to burn out. Additionally, unmeasured conditions like past trauma could have influenced the biological markers.
The study, “Association of internet addiction symptoms with hair cortisol and hair testosterone concentrations,” was authored by Hideki Tsumura and Shuhei Izawa.
