Congestion is the dilation of vessels that supply blood to an organ, caused by an excess concentration of blood. The congested zone often appears red and more or less warm. Congestion is generally benign and can have several causes. Passive congestion, or blood stasis, is when the blood accumulates because of an obstruction to its circulation, such as in thrombosis, or of a mechanical defect not permitting its flow, as in the case of valvular incontinence of veins belonging to the lower limbs, responsible for varicose veins. Congestion may also be active, generated by the influx of blood in an organ or in a zone of irritation or from an inflammatory process. Nasal congestion means respiratory blockage of the nose due to an accumulation of secretions.