Depression is one of the most common mental health disorders in the United States, with 17.3 million adults (7.1 percent of the adult population) and approximately 2.3 million teens (9.4 percent of the adolescent population) diagnosed with the disorder, according to the National Institute of Mental Health. The Diagnostic and Statistical Manual of Mental Disorders identifies depressed mood or loss of interest or pleasure as the two primary symptoms of major depressive disorder for adults. In teens, however, depression can present as excessive irritability and avoidance. What’s more, the teen years are marked by shifting emotions as adolescents grow and change, and this can make it difficult to spot the symptoms of depression. RELATED: Depression Signs, Symptoms, Latest Treatments, Tests, and More Teen depression is more than just feeling blue. In fact, many teens struggling with depression don’t even identify as sad or down. Teen depression wears many disguises, and symptoms can fluctuate. Depression is a serious mood disorder that can affect the way a teen thinks, feels, and acts; and it can impact school performance, family relationships, and social relationships. It helps to take a closer look at how depression affects teens across multiple areas of their lives in order to better understand the symptomatology.

Depression Can Manifest as Physical Symptoms

Teens are more likely to describe physical aches and pains than emotional pain when attempting to communicate their feelings. They can experience a range of symptoms that negatively affect their ability to attend and focus in school, their relationships, and their daily living skills. Psychosomatic complaints tend to be the initial symptoms identified by teens. It can be difficult to recognize these complaints as actual symptoms, as many of them mimic the normal aches and pains of growing up and coping with average stress levels. Psychosomatic complaints are a combination of physical vulnerability and psychological factors. Stress, anxiety, and depression, for example, can cause headaches, stomachaches, and other physical pains. The opposite is also true. Chronic pain can trigger symptoms of anxiety or depression. If psychosomatic symptoms are reported regularly over a period of two weeks or more, take notice. A headache now and then is to be expected; frequent headaches are a red flag. Watch for the following physical complaints from your teen:

HeadachesStomachacheLoss of appetite or other significant change in eating habitsMuscular pain (including stiff neck and other pains)Fatigue

Sleep Disturbance Is Common in Depressed Teens

Though depression can make teens want to hide in their rooms all day, they won’t necessarily sleep. Teen depression is associated with sleep disturbance, including insomnia and hypersomnia. Some teens are up all night due to insomnia, only to sleep during the daylight hours. Others find that they struggle to stay awake, no matter the time of day. Depression can also include interruptions during the sleep cycle. Your teen might fall asleep just fine but wake up during the night and struggle to get back to sleep. As with physical symptoms, it’s important to look for patterns in sleep disturbance. Because of academics, sports, extracurricular activities, and daily stress, teens can have erratic sleep schedules. Sleep disturbance becomes problematic when it’s ongoing and negatively affects your teen’s ability to go to school and attend to normal daily activities.

Watch for Cognitive and Emotional Changes

Depression can affect attention, focus, and memory. You might notice that your teen is more forgetful than usual. They might complain of having difficulty concentrating in school or even when engaged in relaxing activities like reading, video games, or watching TV. While the big red flag for adults is depressed mood or loss of interest, teens are far more likely to exhibit overwhelming irritability or anger. You may also notice significant shifts in moods. While the teen years can include mood changes without warning, moods that appear intense are warning signs of something more than growing pains. Anger is not the only emotional change teens experience when confronting depression. Watch for any of the following changes in your teen over an extended period of time:

IrritabilityAngerDepressed moodFeelings of guiltFeeling helpless (“I can’t ever get my grades back up. It’s too late.”)Feelings of hopelessness (“I’ll never get into college. I have no future.”)Pervasive feelings of sadness or unhappinessFeeling worthless or like a disappointmentFrequent cryingSuicidal thoughts or behaviors

Behavioral Changes and Mood Disorders

Some teens rely on maladaptive coping strategies when dealing with depression, and it’s important to think about how changes in behavior can be attributed to mood disorders. Instead of focusing solely on consequences for negative behaviors, it helps to look beneath the surface and think about what the behaviors may communicate. RELATED: Understanding Suicide Watch for these behavioral changes as potential red flags for teen depression:

Drug or alcohol useReckless behavior (such as driving too fast or having unprotected sex)Missing schoolSkipping out on important appointmentsIgnoring self-care (appearing unkempt, not showering regularly, or refusing regular medications)Social isolationRefusing to participate in normal daily activitiesFighting with family and friendsSelf-harm (cutting, eating disorders)Poor gradesVaping or smoking cigarettes

No two teens are the same, and you know your teen’s baseline. If you feel that something is off, it probably is. It’s always better to seek an evaluation than to wait and see. When teens rely on negative coping strategies, their depression can worsen. If they get the help they need, they can learn to cope with and manage their symptoms and live healthy, fulfilling lives. Remember that the consequences of depression left untreated can be life threatening. Suicide is the second leading cause of death for young people between the ages of 15 to 24, according to the American Psychological Association. If you or someone you know has thoughts of suicide, seek immediate help from the National Suicide Prevention Lifeline at 800-273-8255. Katie Hurley is the author of The Depression Workbook for Teens: Tools to Improve Your Mood, Build Self-Esteem, and Stay Motivated.