Inquire question for this cycle: Is there a relationship between depression and facial appearance?
The focus of this round: Why people get depression?
Firstly, let us get know about depression first. Click the video below to have a brief understanding.
In summary, depress is a mood which will continue for a while or a few hours; MDD(Major depressive disorder, we usually called depression) organized that maintain at least two weeks of low mood that is present across most situations.
Depression is a worldwide mental disease which might occur among both children and elder. Lots of things influence whether a person gets depressed. Some of it is biology — things like our genes, brain chemistry, and hormones. Some is the environment, including daylight and seasons, or social and family situations we face. And some is personality, like how we react to life events or the support systems we create for ourselves. 
Research shows that depression runs in families. Some people inherit genes that contribute to depression. However, not everyone who has a family member with depression will also get it. Besides, many people with no family history of depression still get depressed. Hence, genes are one factor, but they aren't the only reason to cause depression.
- Brain Chemistry
Chemicals called neurotransmitters to help send messages between nerve cells in the brain. Some neurotransmitters regulate mood. When a person is depressed, these neurotransmitters might be in low supply or not effective enough.
- Stress, Health, and Hormones
Things like stress, using alcohol or drugs, and hormone changes also affect the brain's delicate chemistry and mood.  Stress is the body’s response to physical or emotional demands. Emotional stress can play a role in causing depression or be a symptom of it. A stressful situation can trigger feelings of depression, and these feelings can make it more difficult to deal with stress. For instance, losing a family member, divorce, losing a job, all might cause depression.
Daylight and Seasons
Daylight affects how the brain produces melatonin and serotonin. These neurotransmitters help regulate a person's sleep–wake cycles, energy, and mood. When there is less daylight, the brain produces more melatonin. When there is more daylight, the brain makes more serotonin.
Shorter days and longer hours of darkness in fall and winter may lead the body to have more melatonin and less serotonin. This imbalance is what creates the conditions for depression in some people — a condition known as seasonal affective disorder (SAD). Exposure to light can help improve mood for people affected by SAD.
- Female Sex Hormones
It has been widely documented that women suffer from major depression about twice as often as men. Because of the incidence of depressive disorders peaks during women's reproductive years. Women are especially prone to depressive disorders during times when their hormones are in flux, such as around the time of their menstrual period, childbirth, and perimenopause. In addition, a woman's depression risk declines after she goes through menopause.
In summary, there are lost of things might cause a negative mood, but only when this depressed feeling continues for more than a few days, the depression will appear.
- “Why Do People Get Depressed?” Edited by D'Arcy Lyness, KidsHealth, The Nemours Foundation, Aug. 2016, kidshealth.org/en/teens/why-depressed.html.
- “Biology of Depression - Neurotransmitters.” Child Development & Parenting: Infants (0-2), www.gracepointwellness.org/5-d...on-neurotransmitters.
- Some people think they have a clear sense of why they become depressed. Others don't. It might not be easy to figure out. “Common Causes of Depression.” WebMD, WebMD, www.webmd.com/depression/common-causes-depression.
- Schimelpfening, Nancy. “There Are Many Factors That Could Increase Your Risk of Depression.” Verywell Mind, Dotdash, www.verywellmind.com/common-ca...f-depression-1066772.