Depression can be common among people with PTSD and can also occur in family members of those with PTSD. Trauma may involve dangerous events. When this happens it could cause a person to lose faith in their own beliefs of safety and security.

Trauma may also shatter one's beliefs about what is right or wrong, good or bad, and just or unjust. This can lead to negative views about the world, other people, and the future resulting in depressed mood.