The lymph system is a network of lymph nodes, lymph ducts, lymph vessels, and organs that produce and move a fluid called lymph from tissues to the bloodstream.
The lymph glands, or nodes, are small structures that filter the lymph fluid. There are many white blood cells in the lymph nodes to help fight infection.
Lymphadenitis occurs when the glands become enlarged by swelling (inflammation), often in response to bacteria, viruses, or fungi. The swollen glands are usually found near the site of an infection, tumor, or inflammation.
Lymphadenitis may occur after skin infections or other infections caused by bacteria such as Streptococcus or Staphylococcus. Sometimes it is caused by rare infections such as tuberculosis or cat scratch disease (Bartonella).