When Alex Crotty was 11, she felt a profound sense of emptiness. She didn’t connect with her peers. She experienced loneliness and grappled with negative thoughts, but she didn’t know why.

“I didn’t feel unloved. I just felt numb to the world,” she told NBC News in 2017. “Like, I was surrounded by great things, but I just couldn’t be happy.”

Alex was grappling with major depression, a mental health condition that causes people to persistently feel sad or isolated. This mental illness can result in young people avoiding hobbies, struggling academically and experiencing sleeping or eating problems.

Alex isn’t alone in her struggles.

Depression is prevalent among teens today. According to the latest National Survey on Drug Use and Health (NSDUH), about 13 percent of adolescents ages 12 to 17 reported in 2017 of experiencing a major depressive episode in the past year. A major depressive episode is characterized by changes in mood, thoughts or behaviors that prevent people from performing everyday tasks.

Mental illness is an epidemic in the United States, and the NSDUH report indicated that teens were the age demographic most affected by mental health problems. Untreated mental illness can harm a person’s physical health and exacerbate their psychological problems.

Comparing Depressive Episodes Among Teens and Adults

In 2017, the rate of teens who had had a depressive episode was nearly double that of adults. In fact, a greater percentage of adolescents experienced a major depressive episode that had used alcohol in the month prior to the survey.

The percentage of teens with a major depressive episode in 2017 was higher than that of any year from 2004 to 2016. These statistics suggest that the rate of mental illness has become more prevalent among young people.

In total, 3.2 million adolescents ages 12 to 17 reported in 2017 of experiencing a major depressive episode in the past year. Among teens who endured a major depressive episode, more than two-thirds had a major depressive episode with severe impairment.

People who deal with a major depressive episode with severe impairment have trouble completing tasks at home, work, school or other areas of life. They have an increased risk of dealing with relationship or financial problems and may also grapple with suicidal thoughts.

Mental illness often develops during childhood. According to the U.S. Department of Health and Human Services, about 50 percent of people with a mental disorder develop it by age 14. However, in some instances, toddlers can experience symptoms of depression. Many adolescents with a mental health problem turn to drugs or alcohol to numb their physical or psychological pain.

According to the NSDUH report, 1.4 percent of teens experienced a major depressive episode and a substance use disorder in the past year. The presence of mental health and substance use disorder, called co-occurring disorders, can significantly damage a person’s overall health and increase the chances of premature death.

How Mental Illness Affects Young People

It can be difficult to identify mental illness among adolescents because young people are often viewed as emotionally immature. Their brains are not fully developed, so they are more likely than adults to exhibit impulsive behaviors and make poor decisions.

However, mental illness is a neurological disease that parents should take seriously. Anxiety disorders are the most common mental health condition among adolescents, affecting nearly 3 in 10 teens today. Children with anxiety often grapple with intense fear, shyness and nervousness.

Depression is the second-most widespread mental disorder among young people.

Many teens with depression do not always seem sad. In many cases, they exhibit irritability, irrationality or anger. Some parents do not take consistent angry outbursts or other negative emotions by their teens seriously, believing that these actions are a product of normal teenage moodiness. As a result, their adolescent’s feelings are not properly addressed.

What Causes Teen Depression?

The causes of teen depression are not entirely known. Several factors that can contribute to depression among adolescents include hormones, biological chemistry, early childhood trauma and learned patterns of negative thinking.

Research has indicated that social media can impact mental health. A study by the University of Pittsburgh found that a link exists between spending time on social media and harboring a negative body image. Being critical of one’s body image can lead to eating disorders, depression or substance use.

Bullying, including cyberbullying, is also associated with mental health problems. According to a 2017 report by the Centers for Disease Control and Prevention, about 19 percent of high school students reported being bullied on school property in the previous 12 months. Teens who are bullied often experience anxiety, depression or post-traumatic stress disorder.

Helping Teens Experiencing Mental Illness

Parents of teens who experience mental illness should seek some form of treatment for their child. Therapy allows young people to speak with a mental health professional about the causes of their psychological distress and ways to avoid situations that bring about negative thoughts. If needed, a physician can prescribe antidepressant medications.

As the rates of depression among people ages 12 to 17 increase in the United States, so too are the percentage of teens receiving treatment. According to the NSDUH survey, the percentage of adolescents who received treatment after experiencing a major depressive episode rose from 40.9 in 2016 to 41.5 in 2017. During that span, the percentage of teens who received treatment after enduring a major depressive episode with severe impairment also increased.

Teens who deal with depression and drug or alcohol abuse could face dire health consequences, which might include addiction. However, many rehab centers nationwide, including Next Generation Village, offer evidence-based treatments to teens with substance use and mental health disorders. Many of these facilities cater to the specific needs of teens and allow them to continue their education while receiving treatment.

Treatment can help people heal. Therapy, in combination with antidepressant medications, has helped Alex Crotty better manage her depression. She implores teens who deal with depression to tell an adult about their mental health problems and seek professional assistance.

Asking for help doesn’t make people weak, Alex says. It makes them strong.