Depression can be genetic and run in families. Families of people with depression are more likely to have a child with depression. Biological differences get passed down. However, this is not always the case.

There are physical brain differences and functional differences. More research is needed to explain these differences.

Brain function is the way your brain processes information. Depression impacts the neurotransmitters that interact with neurocircuits that maintain mood stability.

The neural networks that support normal emotional behavior play a role in depression. Neuroimaging shows that those with mood disorders have evidence of neuropathological and lesion analysis studies. These networks involve many areas of your brain, including your prefrontal cortex, amygdala, and hippocampus. There can also be alterations in the volume of your grey matter.

Depression is often a symptom of a physical condition that causes an emotional response.

Changes in your genes can cause depression. Your genetic makeup and its interaction with your environment can contribute to your depression.

Studies in 2022 disproved the brain chemistry theory for depression (the monoamine hypothesis). No supporting evidence links depression to serotonin levels in the brain.

Medical professionals are not questioning antidepressants with the debunking of the theory. The chemical imbalance theory came from pharmaceutical companies explaining how their antidepressant products worked, but it never had any hard data to back it up. The theory grew from being repeated over and over until the general public just accepted it. Knowledgeable psychiatrists with a solid understanding of neurology were not so quick to believe there was a connection.

It is still not clear how antidepressants work. This is nothing new. Medications are often used "off label" for other conditions. Sometimes side effects of a medication for one condition are helpful for another illness. The first anxiety medications were antihistamines. Doctors used several common medications for decades without knowing exactly how they worked. Aspirin is one of them.

Some experts don't think there is enough difference between antidepressants and placebos. However, many people experience good results taking antidepressants. On the other side of the coin, some people report antidepressants are no help at all, while others report experiencing harmful effects.

Changes in your environment can cause depression. Stresses, toxicities, and unresolved pain can impact your mood and increase depression. Your learned responses and the development of self-talk are also environmental factors.

Negative thought patterns based on low self-esteem and self-worth, fear of failure, and feeling unworthy can lead to depression. Perfectionism is often at the root of depression. Adverse childhood experiences can also play a role in the development of depression. Children who experience trauma can carry their childhood trauma into adulthood.

Abuse can lead to depression, and depression can lead to abuse. This cycle of pain and suffering is, unfortunately, quite common. Although people often think of abuse and depression as separate issues, a recent study shows a link between the two. The study, conducted by researchers at the University of Toronto, looked at data from over 9,000 adults. The results showed that abused participants were more likely to be depressed than participants who had not been abused. After accounting for other factors such as age, sex, and income, the results still held.

Prescription medications can also cause depressive symptoms. If you are taking prescription medications and feeling depressed, look up the side effects of each one and talk to your doctor or pharmacist. Switching to a different medication can relieve depressive symptoms.

There is increasing evidence that hormones may play a role in the development of depression. Women are more likely to experience depression around the time of their menstrual periods and during pregnancy or after giving birth. An increase in depression during this time suggests fluctuations in hormone levels may be associated with mood changes in some people.

Menopause is another time in life when depression can show up. Women are at higher risk for depression during perimenopause as well. The transition phase when your reproductive hormones are making the change from fertility to the postmenopausal stage can involve several mood changes that can seem to come from nowhere. 

As your menstrual cycle becomes shorter, lighter and irregular hormonal changes are taking place. Serotonin, the happiness brain chemical drops and just this change alone can cause sadness, crankiness, anxiety and irritability. There are so many things going on in your body during "the change" it's no wonder why is can be such a tumultuous time. It can feel like you're on a wild ride at an amusement park being thrown this way and that.

Women are twice as likely as men to struggle with depression. All the stags of life women go through have hormonal changes that lay the foundation for emotional changes. Monthly menstruation changes increase the likelihood of depression too.  Research on the role of hormones in depression is ongoing, and it's still unclear exactly how they contribute.