Lymphocytes are the white blood cells that help to protect our bodies from infections and diseases; lymphoma is a blood cancer which is the result of these cells behaving abnormally. Lymphocytes which begin to behave abnormally may live longer than they are supposed to or divide more quickly than normal cells .
Lymphocytes flow through the body in a clear fluid called lymph; lymph travels through lymphatic vessels which form part of the lymphatic system, which in turn forms part of the immune system. Hodgkin and non-Hodgkin lymphoma are uncommon cancers which develop in the lymphatic system  .
In lymphoma, lymphocytes begin to multiply in an abnormal way, they lose their ability to fight infection, making sufferers more susceptible to contracting infections. The abnormal lymphocytes begin to gather in certain parts of the lymphatic system such as the lymph nodes (glands) .
The most common symptom of Hodgkin lymphoma is one or more painless swellings in the following areas:
These swellings are enlarged lymph nodes. About 70% of people diagnosed with Hodgkin lymphoma have a swollen lymph node in their neck. Lymph glands commonly swell if we have an infection but they then usually go back to normal over a short time. With a lymphoma the lymph nodes often grow slowly and may be there for months or years before they are noticed. But sometimes they grow very quickly .
While swollen nodes are usually painless, some people report that the lumps are painful and some note that that are painful after drinking alcohol.