Traditionally, research has been focused on the development of symptoms in direct trauma survivors. However, during the last two decades researchers and clinicians have started exploring the way individual traumatic stress exposure affects trauma victims' spouses, children and professional caregivers. Studying trauma within the family is a part of what is called systemic traumatology, a study of groups, institutions and other human systems that show stress reactions directly caused by a traumatic event or series of events. The effect of an individual's traumatic stress on family members and on persons in direct contact is conceptualized as secondary traumatisation. In its narrow sense, secondary traumatisation involves a transfer of nightmares, intrusive thoughts, flashbacks and other Posttraumatic Stress Disorder symptoms, which are typically experienced by individuals suffering from PTSD, onto their immediate surroundings. In its broader sense, the term refers to any kind of distress transfer from a trauma victim to their immediate surroundings, and includes a broad spectrum of distress manifestation along with that resembling Posttraumatic Stress Disorder. Beyond that, a family member's PTSD is potentially transferable to subsequent generations, interfering with the psychological development of children.