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10 Scientific Reasons You’re Feeling Depressed

Is depression caused by hormones, lifestyle, expectations, or all of the above?

Key points

  • Research suggests that differences in the way our brains process a chemical called galanin may make some of us less resilient.
  • Perimenopause as well as the thyroid gland can both cause hormonal issues that influence mood.
  • Non-chemical causes of depressions include childhood trauma and the cumulative effect of negative ruminations.
Source: Aleshyn_Andrei/Shuttersock

Are you waking up most days just feeling “blah?" Perhaps you don’t want to do anything except lie like a couch potato and watch TV—and even that is unsatisfying. You not only feel low energy but kind of miserable. Perhaps you’re mad at yourself for not getting the house cleaned, not getting your work done, or not getting those papers filed. Perhaps you’re feeling a bit lonely, left out by friends, or unsupported by family. You may dwell on mounting bills or the fact that you’re 10 or 20 pounds overweight. You may feel aches and pains in your neck or back. Or you may just feel grouchy and want to remain undisturbed by life’s demands and conversational opportunities. You may compare yourself unfavorably to your friend, roommate, cousin, or neighbor, who always seems to be on time, well-groomed, and on track to meet her goals. We all have those “blah” days—but why do they happen, and what can we do about them? Below are 10 scientific reasons why you may be feeling out of sorts.

Brain Chemicals

Some of us have brains that are more sensitive to the effects of stress. Researchers are just beginning to uncover the biochemistry behind this differential. The most common forms of antidepressants target the neurotransmitters serotonin and norepinephrine because some research concludes that low levels of these chemical motivators are part of what makes us depressed. However, only some people respond well to the most common forms of antidepressants, while others try drug after drug with no substantial mood improvement. A recent research study, published earlier this year in Proceedings of the National Academy of Sciences, may reveal the reason why. The research suggests that differences in the way our brains process a chemical called galanin may make some of us less resilient and able to bounce back after difficult experiences.

The Weather

Less sunshine during the winter months can give us the blues, and this effect is more pronounced for some people than others. Researchers Keller and colleagues studied hundreds of people and found that during the spring, moods improved; participants also reported more outdoor activities. We may also be more cognitively flexible and able to think creatively about solving our problems in the spring, compared to winter. A subgroup of people suffer from Seasonal Affective Disorder, a condition in which the winter blues turn into full-blown depression along with associated changes in sleep, appetite, and motivation. Sufferers are more likely to be women. Exposure to outdoor sunlight also provides us with vitamin D, a substance with clear links to depressed mood.

Vitamin D

Most people in the US have insufficient or deficient levels of Vitamin D. The reasons are not clear, but could be related to nutrition and insufficient sun exposure. People with dark skin are more vulnerable to vitamin D deficiency, due to a decreased ability to process vitamin D from sunlight. Vitamin D deficiency has been statistically linked to depression. In a large Dutch study by Hoogendijk and colleagues (2008) of over 1,200 persons aged 65 and older, levels of vitamin D were 14 percent lower in persons with minor or major depressive disorder when compared to those not showing depressed mood.


Hormones are substances produced by the endocrine glands that influence many bodily functions, including growth and development, mood, sexual function, and metabolism. Levels of certain hormones, such as those produced by the thyroid gland, can be factors in depression. In addition, some symptoms of depression are associated with thyroid conditions. Hormones fluctuate during the menstrual cycle and may create vulnerability to sad or depressed moods in the premenstrual period, as well as during perimenopause, and menopause. There are individual differences in how much our moods are vulnerable to the effects of hormones. If you are more vulnerable, you may want to consult a physician to see if medications are needed to help regulate your hormones. You could also try alternative medicine treatments, such as acupuncture, to reduce hormone-related mood imbalance.


Our moods are not only a function of what happens to us, but also of how we view the events in our lives and the meanings we assign to them. There are stages in most of our lives in which we seem to be working hard and doing all the right things, but don’t see many external rewards coming our way. We may not be paid what we feel we are worth or be able to afford as nice a house, car, or vacation as our friends. We may struggle to find the right partner, while our friends or siblings seem to have no problem finding love. We may have to work longer and harder than our friends to get the same grade on a test or earn a living. We may experience a difficult breakup or loss. Life naturally isn’t fair; periods of struggle, suffering, and loss are inevitable. If we expect fair or special treatment all the time or expect things never to change, we are bound to be disappointed. So if you’re feeling sad because of recent events, remind yourself that hard times are part of life and will pass. You can also try to deliberately broaden your view and focus on the good parts of your life or the experiences you are proud of.

Childhood Adverse Events

Stressful life events can wear down our physical and mental resources, making us more vulnerable to both depression and physical illnesses. A history of childhood trauma, including abuse, poverty, or loss of a parent, can reset our developing brains to be less cognitively flexible. It seems that our brains naturally go into a “fight, flight, freeze” response to stress or a threat, and we often have to use our prefrontal cortex or executive center to get out of this state. Prolonged stress in childhood can make our brains less interconnected and resilient; our brains can more easily get “stuck” in negative thinking patterns or stressed out states, resulting in us being less able to change tracks.

Stresses Piling Up

As Robert Sapolsky argues in his book, Why Zebras Don’t Get Ulcers, our human stress response systems were designed to respond to acute, time-limited stressors that normally require a physical response. When our ancestors had chased off that marauding tiger, they could relax and eat. The stressors in today’s world are much more chronic and less able to be controlled by taking action, and we often don’t get the break afterward to recover and regroup. Financial stress, loneliness, constant fighting with loved ones, being bullied, long commutes, academic or job demands, or unemployment can drag on, triggering a cascade of effects across many areas of our lives. When stresses hit us one after the other without time for recovery, they can leave us depleted and despondent, with insufficient pep to bounce back.

Negative Ruminations

You may be feeling bad because you’re sitting around brooding about life’s disappointments or trying to find a reason why things aren’t going your way. Research studies by University of Michigan psychologist Susan Nolen-Hoeksema and colleagues show that sitting around thinking about your negative mood or negative events just makes everything worse. One negative thought leads to another, and then another—until you get buried in a mountain of problems and negative predictions. This can easily lead to a loss of perspective and motivation, one that can interfere with actually taking action aimed at addressing the problem. If you find yourself in a negative thinking cycle, get up immediately and do something else pleasant or neutral to engage your mind. This can be as simple as emptying the dishwasher, rearranging your closet, going for a walk, talking to a friend, or getting on with a work project.

Your Inner Critic

Do you have a critical inner voice constantly judging and criticizing everything you do, especially when things don’t go your way? The inner critic compounds the effect of anything negative in your life by blaming you for it. It keeps drawing your attention to the negative and spoils your pleasure when something positive happens by telling you that ”it won’t last” or “you don’t deserve it." This negative dialogue takes you out of the moment and makes you feel depressed. Negative thinking can be a symptom of depression and may be a causal factor in interaction with negative life events.

The first step to combat an inner critic is to become aware of what it’s saying; the second step is to externalize it. You could give your critic a name and imagine what it looks like—picturing it as a grumpy old crone, for instance, or a vicious barking dog. Then begin talking back to it, and telling it to back off. The inner critic generally has a negatively biased perspective and overestimates your responsibility for—and control over—outcomes in your life. It also often has perfectionistic expectations. Tell it to give you a break for a change!


Our human brains are wired to be part of a social group, and we experience loneliness as chronically stressful and depressing. Unfortunately, some of us have toxic or neglectful families that don’t provide support or presence when we need it. Similarly, we may feel that our friends are moving on—finding romantic relationships or having kids, for instance—and leaving us behind. Research using fMRI brain scans shows that even minor social rejection lights up the same areas of our brains as physical pain. Feeling left out, rejected, or excluded makes us sad; it can also lead to rumination about our faults, further darkening our moods. We become scared of further rejection and isolate ourselves, perpetuating the negative cycle. While there may not be an immediate cure for loneliness, it helps to get out in the world and pursue your natural interests, which can lead to expanding your social network. Staying in touch with old friends or family and deliberately seeking opportunities to connect may help as well.

Final Thoughts

The reasons for a down mood are often multifaceted and can be difficult to determine. If you feel depressed for two weeks or more, seek a medical consult to rule out or treat underlying biological factors. Consider consulting a mental health professional for help in managing stress and expectations, negotiating life changes, or dealing with the emotional aftereffects of past traumas and dysfunctional families. If you can’t afford therapy, antidepressants may still help to change the underlying biology. Exercising outdoors can provide both sunlight and mood elevation. Develop a toolkit of stress-reducing activities, such as regular exercise, yoga or meditation, watching funny movies, playing team sports, doing something creative or novel, and hanging out with and/or confiding in understanding friends.

To find a therapist, please visit the Psychology Today Therapy Directory.

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