Facebook is an internet social network website designed to keep people in touch in a more modern way than in years past. Before the convenience of the internet, people kept in touch by writing the occasional detailed letter to one another and would sometimes enclose photos of their life events to catch up to speed on what was going on their lives. Since Facebook came along, you can easily keep up with a multitude of people who are close friends and/or acquaintances in your own personal "friends" list, by posting "status updates" at your leisure (some people post daily) or when you choose to. You can even upload photos of your family members, your great vacation, what you're thinking, or just what you're doing (or thinking about doing) that moment in a day. With that being said, people tend to post status updates that are going to paint the best picture of their so called "perfect life". For certain individuals, especially ones with low self-esteem this can cause a mild form of depression, because they don't feel as adequate or that their life is as great as their Facebook friends.
An additional mismatch theory – one that is compatible with the social competition theory – is the "social risk hypothesis" of depression (Allen & Badcock, 2003, 2006). This theory proposes that mild depression is an adaptive response that evolved to aid risk aversive behavior in social contexts; for example, in threat situations, the suite of depressive functions include hypersensitivity to the social status of others, reducing one's expectations of success and sending signals of low relative self-value to others. This theory is when people grow up in front of violence, witness excessive volatile behavior, adhere to sexual harassment or go through a negative life event (such as losing a loved one). Most accounts acknowledge that sadness and mild depressive states perform psychological functions but that depressive illness occurs when this functions, is dysregulated resulting in "major depression" (Hagen, 2011 p.