The lymph glands of the body represent an important site for the production of protective cells aimed at overcoming systemic infections. However, during infections it is common for a few or many lymph glands to become involved, swollen and tender. This is due to their overproducing their normal products, or else to being involved in the general infective process.

Often an infection in the mouth (ulcer of the tongue or inside of the cheek) will produce a very tender swelling under the jaw. Simple herpes infections around the mouth will produce similar lymph-gland swelling. Many glands throughout the body may swell as viruses spread throughout the system, such as in glandular fever.

However, the lymph-gland system may also become caught up with malignant changes, for the lymphatic drainage system of the body is a widespread, interconnecting network. Often lymph glands may become involved, even though they may be quite a distance from the original cancer site. When disease of the lymph glands is present, the doctors will usually make a vigorous search for the primary site of the disease.