It must be reason. For that, the most common are: 1-nfection. 2-virus. 3-inflammation: infiltration with inflammatory cells during infection or inflammation in a region of a given lymph node. 4-cancer. 5-cancer of the blood: uncontrolled, malignant multiplication of lymphocytes as in lymphoma or leukemia.
Monitoring Centers. Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells/digested food. Lymph nodes "taste" the lymph everywhere for bad stuff like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.
Many possibilities.. Possible causes are: 1) infection- viruses, e.g., mono, herpes, hiv; bacteria e.g., strep, staph, etc; inflammation from autoimmune disorders 2) primary malignancies e.g., lymphoma, hodgkins 3) secondary malignancies e.g., metastatic cancers- breast, lung cancer, others 4) rare inherited metabolism disorders 5) rare poorly characterized disorders e.g., angioimmunoblastic lymphadenopathy.
Medical eval. Global lymphadenopathy is not normal. Recommend medical assessment to know.
Lymphadenopathy. If lymph nodes are sufficiently enlarged they can impinge upon and obstruct passages otherwise open, extend their disease (if any) into adjacent structures or damage them with pressure. Much of this obviously depends upon the cause of the lymphatic enlargement. If this is malignancy it is very different than reactive lymphadenopathy. Good luck.