*Damage to veins
–Usually caused by a central line (a device inserted by a medical professional to provide direct access to the blood for giving medication or drawing blood)
* Poor blood flow in the veins. This occurs with immobility from a hospital stay.
* Genetic blood clotting conditions
* Illnesses like cancer, intestinal disorders, and serious infections of the blood, throat/neck, and bones.
* Congenital heart disease
* Autoimmune disorders
* Birth control medications–increases the risk in teenage girls
* Certain medications