EDITOR'S NOTE: This is the second in a series of Athens Banner-Herald stories on parenting troubled teens.

Mental illness is prevalent in the U.S. and teens are not excluded from the diagnosis of a mental disorder.

In 2011, there were an estimated 9 million adults aged 18 or older with a serious mental illness, which represents about 3.9 percent of all U.S. adults, according to the National Institute of Mental Health.

Many psychologists believe that mental illness begins and can be treated at an early age, specifically the teen years.

Four million adolescents in the country suffer from a serious mental disorder, according to the National Alliance on Mental Disorders.

For children ages 9-17, 21 percent have a diagnosable mental or addictive disorder that causes at least minimal impairment, according to NAMI. Those illnesses may cause significant functional impairments at home, school and with friends.

Athens Dialectical Behavior Therapy Center director and social worker Iain Halstead specializes in treating teens who suffer from ailments such as borderline personality disorder, one of many mental disorders.

"It's seen more these days as an emotion regulation disorder. Certain people have great difficulty managing their emotions and often cannot calm themselves down," Halstead said. "Borderline personality disorder really refers to a set of behaviors that people use to try to manage their unmanageable emotions. These can be self harming behaviors, alcohol or drug use, sexual acting out or anything else that might work to change a particular unwanted emotion such as distress or anxiety, shame or sadness."

Although there are multiple avenues parents can take to treat their teen who has an emotional disorder, Halstead recommends the DBT approach.

"DBT is a three-pronged approach to tackling emotion-driven behavior. First ... it teaches a package of skills that individuals can use to deal with their difficult emotions. Some skills are specifically for getting through the night when you feel like self harming, others are for decreasing and regulating big difficult emotions," Halstead said. "Others teach communication skills so that individuals can set limits without feeling guilty or deal with relationship conflict without making the situation worse."

Secondly, DBT helps individuals understand how to apply the skills to their specific situations, Halstead said.

"It analyzes a person's behaviors and helps them understand the triggers to their actions so they can begin to change patterns of behavior," he said. "And thirdly, it provides 24/7 phone and text coaching and support for those moments when the emotions are so large or the situations so overwhelming that it's difficult to know what to do or which skills to use."

Halstead said there are many signs a teen might exhibit if they are dealing with a mental disorder or other emotional problem. In depression a teen may exude a pervasive or sad mood for an extended amount of time, or possibly a distinct loss of interest or difficulty becoming interested in things a person might normally engage in such as shopping, sports, music or hobbies.

"In teenagers there may also be a lot of irritation or anger," said Halstead. "Overwhelming tiredness or fatigue will often show up, as will changes in weight or failure to make expected weight gains. Anxiety in teens may show itself in a desire to avoid being around others or to avoid school."

Halstead said that teens exhibiting early signs of BPD might also have symptoms of depression or anxiety in combination with mood swings or problems managing anger.

"They're more likely to get into interpersonal difficulties as well," he said. "And could have difficulties making and maintaining friendships."

Another result of emotional stress can be self harm, according to Halstead.

"Often it relates to fear of rejection or abandonment and this can come about when they feel guilt because they've gotten into an argument and haven't been able to control their own emotions and may have said something hurtful," Halstead said. "Not being included in peer group plans can cause huge anxiety related to rejection. Break-ups with boyfriends or girlfriends or bad grades can cause big emotions that lead to self harm."

Halstead said that self harm is often a way for a teen to deal with emotional pain.

"Sometimes painful situations that seemingly can't be resolved can be dealt with by cutting. Sometimes emotional situations cause pain that can't be understood but can be felt physically with cutting. Sometimes cutting is self punishment," he said. "But it's rarely a cry for help and should not be confused with an attempt at suicide. ...

"In all of this, it's probably important to recognize that some behaviors are normal teenage behaviors. It's expected that teenagers will push boundaries, be argumentative or sulky. They may also experiment with alcohol or drugs and sex. It's important not to pathologize these behaviors and think that everything needs some kind of treatment. The best thing a parent can do is to talk to their teen about their life, and perhaps most importantly, to listen to their teenager."

• Follow breaking news reporter Allie Jackson at www.facebook.com/AllieJacksonABH or www.twitter.com/Allie_ABH.