What Is Mental Illness?
Wellness & SelfcareMental Health

What Is Mental Illness?

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Updated on March 23, 2026
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Mental health is the facet of your health that focuses on your emotional and psychological well-being. It influences how you think, feel, and act. But just like how your body can get a physical illness, your mind can experience a mental health condition.

How exactly do you know when your mental health is negatively affecting you? New York-based clinical psychologist and author Roberta Temes, PhD, says: “If it interferes with your relationships, your work, your sleep, your daily feelings of contentment, or if it negatively impacts someone else, it’s a problem. And if it doesn’t interfere with any of that, it isn’t a problem.”

Here’s everything you need to know about mental health and mental illness, including signs to look for, how a diagnosis occurs, and treatment options.

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Symptoms of Mental Illness

Knowing the symptoms of mental health conditions is important. It can help you understand when you should reach out to a professional for medical support. If you’ve noticed one or more of the following changes to your thoughts, feelings, or behaviors, talk with your primary care provider or mental health professional:

  • Not coping or functioning as well as you once did
  • Excessive worrying or feeling anxious a lot of the time
  • Fast mood changes
  • Trouble concentrating or feeling confused
  • Feeling sad, down, or hopeless most of the time
  • Not able to stop thinking about past or recent upsetting events
  • Avoiding social situations and your relationships
  • Coping with substances like alcohol or drugs
  • Not sleeping well or feeling exhausted during the day
  • Often irritable, hostile, or prone to anger outbursts
  • Prone to extreme fears that keep you from doing things you’d like to do
  • No longer enjoy the things that used to make you happy
  • Serious thoughts of suicide or self-harm

If you’re in distress now, you can receive free and confidential support by dialing 988 for the National Suicide Prevention Lifeline. It’s available 24 hours a day, seven days a week. If you’re in crisis and need urgent help, call 911 or go to the emergency room.

Having mental health concerns can feel scary, anxiety-inducing, or even frustrating. Please remember that you are not alone. Mental health conditions are becoming increasingly common, and healthcare providers can help.

How Is Mental Illness Diagnosed?

Determining whether an emotion, a behavior, or a combination of the two is affecting your health enough to be labeled a mental health condition can vary from person to person. “Different people can deal with the same level of problem very differently depending on their resilience and coping skills,” explains James Maddux, PhD, a professor emeritus in the department of psychology at George Mason University and a senior scientist at the university’s Center for the Advancement of Well-Being.

“There is no hard and fast line between normal emotions and problems of living, of thinking, and behaving in ways that cause emotional distress or upset. There’s such a tremendous gray area between the two that that distinction does not exist.”

So what should you do if you feel like your mental health is changing and you need some support to figure out what’s going on? The best first step is to reach out to your healthcare provider for a physical exam and mental health screening. Your provider can help you understand if your symptoms are due to a physical health condition. If not, they can refer you to a licensed mental health professional for a psychiatric evaluation.

If you’re seeing a psychiatrist or psychologist, they’ll likely turn to The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), which lists criteria for all mental health conditions. Your mental health professional can also offer various psychological assessments to identify which symptoms or illnesses you may have.

It’s important to recognize that a diagnosis provides only a broad label for your symptoms. “It doesn’t automatically point the way to a cure,” says Maddux. “It’s individual in the eyes of the person experiencing the problem and also in the eyes of the professional who’s evaluating the person’s emotional distress or behavior problem. Everyone’s experience is different.”

A diagnosis is simply a starting point from which you and your clinician can begin to formulate a treatment plan tailored specifically to your symptoms and overall health needs.

List of Mental Health Conditions

There’s a wide variety of mental health conditions, and all of these affect you a little differently. Here are some common ones to be aware of:

Anxiety

Reacting to difficult situations or negative news by worrying or feeling nervous can often feel like a universal experience. Feeling apprehensive or fearful is even healthy when it helps you avoid potential harm. But if those thoughts are making you terribly uneasy, interfering with day-to-day activities and relationships, or causing dizziness, racing heart, or other physical symptoms, you may be living with an anxiety disorder. However, treatments like therapy and anti-anxiety medications can help you cope.

Learn More About Anxiety

Bipolar Disorder

Living with any mental illness can be challenging, but bipolar disorder can be especially so. One reason bipolar disorder poses challenges is that it isn’t always easy to get an accurate diagnosis. One feature of bipolar disorder is unpredictable mood swings between two opposite symptoms, depression (periods of feeling sad, hopeless, or lethargic) and mania (periods of euphoria, high energy, and impulsivity). Bipolar disorder also has three subconditions called bipolar I, bipolar II, and cyclothymic disorder, which can sometimes make it difficult to be diagnosed correctly. An experienced mental health professional, however, can make an accurate diagnosis and develop a personalized treatment plan that helps reduce symptoms and improve quality of life.

Learn More About Bipolar Disorder

Depression

Depression is one of the most common mental health conditions. However, it’s also one of the most undertreated ones since many of the signs of depression — such as feeling sad, irritable, overwhelmed, or hopeless — can easily be chalked up to everyday stress. Other common symptoms of depression include difficulty doing daily activities, losing joy in things that used to make you happy, or feeling as though life isn’t worth living. Treatment may include therapy, medications, or lifestyle changes.

Learn More About Depression

Borderline Personality Disorder

When most people feel intense emotions like sadness or anger, coping mechanisms kick in to keep their reactions in check. But for people with borderline personality disorder (BPD), they often find intense emotions so painful and difficult to contain that they may go numb, feel frantic, or do potentially harmful things like act out in a rage, drive recklessly, eat uncontrollably, or even injure themselves or attempt suicide. However, treatment is available, and with the right medications, therapy, and social support, people with BPD can regain emotional control and improve their quality of life.

Learn More About Borderline Personality Disorder

Post-Traumatic Stress Disorder

PTSD can develop in anyone who has witnessed or experienced a traumatic event, including but not limited to an accident, abuse or violence, or natural disasters. This condition may cause symptoms like feeling emotionally numb, frequently having nightmares or flashbacks, or experiencing extreme anxiety, which can make it feel difficult to function. But processing your feelings through various therapy options, developing helpful coping skills, and implementing certain lifestyle changes can help you move forward after experiencing trauma.

Learn More About Post-Traumatic Stress Disorder (PTSD)

Schizophrenia

Hearing sounds that don’t exist, seeing things that are not there, or living with paranoid thoughts are all classic signs of schizophrenia, which is a brain disorder that usually appears in late adolescence or early adulthood. This condition is linked to a chemical imbalance in the brain, as well as environmental and genetic factors. And while more research is still being conducted, antipsychotic drugs and psychosocial therapy can be effective in managing symptoms.

Learn More About Schizophrenia

However, there are several other mental health conditions that you may experience that aren’t listed here. So, if you notice changes in your emotional well-being, see a healthcare provider. They can help you understand what you’re going through, do tests to identify your symptoms, and make a diagnosis. Then they can offer treatment options or give you a referral to a specialist, and support you with your mental health journey. Help and hope are available; please don’t forget that.

The Takeaway

  • Mental health conditions are common, and you’re not alone in your journey.
  • Symptoms like excessive worry, feeling sad or hopeless, or trouble sleeping can be a sign to reach out for professional help.
  • If you notice changes in your thoughts, feelings, or behaviors, see your healthcare provider for a diagnosis.
  • Your exact treatment plan will differ based on the symptoms you have. But the goal of treatment across all mental health conditions is to improve your functioning and overall quality of life.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. What Is Mental Illness? American Psychiatric Association. July 2025.
  2. Warning Signs and Symptoms. National Alliance on Mental Illness.
  3. Anxiety Disorders. Mayo Clinic.
  4. Bipolar Disorder. Mayo Clinic.
  5. Depression (major depressive disorder). Mayo Clinic.
  6. Depression Borderline personality disorder. Mayo Clinic.
  7. Post-traumatic stress disorder (PTSD). Mayo Clinic.
  8. Schizophrenia. Mayo Clinic.
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Lee S. Cohen, MD

Medical Reviewer
Castle Connolly Top Doctor, From NewYork-Presbyterian

Lee S. Cohen, MD, is an associate professor of clinical psychiatry at Columbia University Irving Medical Center, maintains a clinical practice focused on expert and complex diagnostics, and is considered an international expert in clinical psychopharmacology. He is also the director of the Clinical Neuroscience Center, involved in innovative development and discovery of new compounds for neuropsychiatric conditions and directly consults with multiple pharmaceutical companies worldwide.

Dr. Cohen graduated from the Sophie Davis Biomedical Education Program at the CUNY School of Medicine at The City College of New York, an accelerated six-year BS/MD program. He then completed his MD at SUNY Stony Brook School of Medicine.

He trained in pediatrics and adult psychiatry at Mount Sinai Hospital in New York City, followed by a fellowship in child and adolescent psychiatry at New York Presbyterian Columbia University Irving Medical Center. He served for 20 years as the director of psychiatry at the Clinical Neuroscience Center at Mount Sinai West Hospital.

He is a senior reviewer for multiple journals, including the Journal of Child and Adolescent Psychopharmacology, the Journal of Developmental and Physical Disabilities, and the International Journal of Autism and Related Disabilities.

Cohen teaches and presents research domestically and internationally at meetings such as those of the American Psychiatric Association and at major universities around the country.

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Nuna Alberts, LCSW

Author

Nuna Alberts, LCSW, has been in private practice for more than 20 years, treating hundreds of adolescents, adults, and couples for depression, anxiety, obsessive compulsive disorder, relationship problems and a range of other issues.

She earned a bachelor's in art history from Columbia University School of General Studies, with an emphasis on criticism, and received a master's in social work from New York University, where she focused on psychodynamic psychotherapy. For her master's in journalism thesis for Columbia University, she wrote about genetic testing and the ethical choices that can arise from it.

Her writing has been published in multiple magazines and national newspapers, and she was the editor and an author of the 2002 book Strengthen Your Immune System: Boosting the Body's Own Healing Powers in the Fight Against Disease. She is currently working on a book about psychotherapists' perspectives on their own psychotherapy.

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