When drainage fails
Because the lymphatic system returns leftover tissue fluid to the blood, a blockage causes fluid to collect in the tissues. This swelling is called lymphoedema. It can follow surgery that removes lymph nodes, injury, or infection, and often affects an arm or leg. The limb becomes puffy and heavy because the trapped fluid cannot drain away. Because the lymphatic system also fights infection, its diseases can weaken the body's defences and lead to repeated infections in the swollen area.
Elephantiasis and infection
A dramatic form of blockage is elephantiasis, part of the disease lymphatic filariasis. Tiny parasitic worms, spread by mosquito bites, live in the lymphatic vessels and block them. Over years the affected leg or other body part swells enormously and the skin becomes thick and hard, resembling an elephant's skin. The condition is difficult to reverse once advanced, which is why prevention through mosquito control is so important in the tropical regions where it occurs.
Example
During an infection such as a sore throat, the lymph nodes in the neck often swell and feel tender. This is normal: the nodes are filtering pathogens and producing extra lymphocytes to fight the invaders.
Cancer of lymph tissue
Lymphoma is a cancer of the lymphocytes and lymph tissue, in which these white blood cells multiply abnormally. Warning signs include painless, swollen lymph nodes, tiredness and unexplained weight loss. Tonsillitis is inflammation of the tonsils, which are lymph tissue guarding the throat; it causes a sore throat and swollen glands and is common in children. Many lymphatic problems are first noticed simply as lumps or swelling, so any lump that does not go away should be checked by a doctor rather than ignored.
Key idea
Prevention and care: control mosquitoes and use nets to avoid filariasis, seek early treatment for persistent swelling, and support drainage after surgery with gentle exercise and movement.