Manual lymphatic drainage (MLD) is a type of gentle massage which is intended to encourage the natural drainage of the lymph from the tissues space body. The lymph system depends on intrinsic contractions of the smooth muscle cells in the walls of lymph vessels (peristalsis) and the movement of skeletal muscles to propel lymph through the vessels to lymph nodes and then beyond the lymph nodes to the lymph ducts which return lymph to the cardiovascular system. Manual lymph drainage uses a specific amount of pressure (less than 9 ounces per square inch) and rhythmic circular movements to stimulate lymph flow.
Manual lymphatic drainage was pioneered by Danish Drs. Emil Vodder and Estrid Vodder in the 1930s for the treatment of chronic sinusitisand other immune disorders. While working on the French Riviera treating patients with chronic colds, the Vodders noticed these patients had swollen lymph nodes. In the 1930s, it was considered taboo to tamper with the lymphatic system due to the medical profession's poor understanding of this system. The Vodders were not deterred by this and, in 1932, began to study the lymph system, developing careful hand movements to cause lymph movement. In 1936, after four years of research, they introduced this technique in Paris, France.
MLD is now recognized as a primary tool in lymphedema management. Therapists can today receive certification through special classes conducted by various organizations specializing in MLD, or through a complete lymphedema treatment certification course. Scientific studies show mixed results regarding the efficacy of the method in treating lymphedema and further studies are needed. A 2009 meta-analysis of studies in the area of sports medicine and rehabilitation showed best evidence of effectiveness for Manual lymphatic drainage treatment to "enzyme serum levels associated with acute skeletal muscle cell damage as well as reduction of edema [swelling] around broken bones."  A 2013 systematic review of manual lymphatic drainage with regard to breast cancer related lymphedema found no clear support for the effectiveness of the intervention in either preventing limb edema in at risk women or treating women for the condition.