Any injury causes pain, which is a stressor on the nervous system, which in turn influences the immune system response. Being injured can suppress the immune system in some people depending upon the extent of injury which causes pain and the duration of the pain, which again is the stressor. Injury triggers stress response by the sympathetic nervous system. The magnitude and duration of pain has a direct influence on the immune suppression or enhancement. The effects of injuries to the immune system of the body can be detrimental or beneficial. However a balanced immune system is strong and prepared to provide immune defense against pathogens. The immune system will not work optimally like it should when there is underlying pain associated with injury and stress caused by the pain. Injury can result in infection caused by the entry of the infectious agent(pathogen) through the skin which can multiply. Immune systems start wound repair as a response to the injury with the help of cells macrophages and neutrophils. Injury can result in pain if persists for weeks or in some cases for months can result in an increase in body's cortisol levels. Adrenal glands produce Cortisol which is a hormone induced by stress in the body. Cortisol plays a crucial role in regulating your immune system. Autoimmune diseases, allergies, regular infections, and inflammation is the results of either too low or high cortisol levels which do alter the immune response. Immune system Chronic stressors caused by traumatic injury which leads to permanent disability can have a negative impact on the immune system by modifying immune system functions because of the long lasting emotional connection to the stress. For long term stressors like chronic pain due to injury and the cortisol might stay elevated long term for months or even years suppresses the immune system and reduce the inflammation. Suppressed immune system makes a person vulnerable to diseases like cold, flu viruses and other pathogens. The ability of the body to fight infections is lowered as a result of the breakdown in immune system function which affects the quality of life of a person. At the moment of injury, the response to trauma caused by the injury begins in the immune system. The immune system responds by producing inflammatory mediators and macrophages. The host response as a result of traumatic injuries disrupts the hemostasis of the immune system resulting in the inflammatory complications and infections. Inflammation occurs at the molecular level at the moment of injury. Injuries affect phenotype of the immune system and response to the injury depends on the severity of the injury, age, genetics and sex of the person. Injuries lower the immune system functions and influence the pathways and immune cells involved in regulating the immune response. Injury and its effects on Immune system: Immune systems respond to the tissue damage caused by the injury very promptly. Cells and mediators of the immune system undergo changes as an immune response to the injury also called SIRS, MARS or CIRS which are pro-inflammatory and counter-inflammatory complex host responses. Injuries induce pro-inflammatory and counter inflammatory immune responses. This changes in the immune system phenotype and it's function disrupts the hemostasis of the immune system which results in patient's predisposition to infections and other inflammatory complications following the injury. The immune system is exposed to cell debris, tissue damage and alarmins the endogenous antigens following injury. Two hit response is another complication to the injury for patients who have severe response to secondary insult in patients which might result in septic shock where patients develop high risk of infections because the innate immune system cells macrophages and neutrophils becomes very reactive to the bacterial toxins resulting in inflammatory cytokines and ROS in a very elevated levels causing systemic inflammation and tissue destruction which is cell mediated.