What Are Lymph Nodes?
Lymph nodes are small, bean-shaped glands distributed throughout the body — with clusters in the neck, armpits, groin, chest, and abdomen. They are part of the lymphatic system and act as filters, trapping bacteria, viruses, and abnormal cells while housing immune cells (lymphocytes and macrophages) that mount the immune response. Normally, lymph nodes are not palpable. When they enlarge (lymphadenopathy), it means the immune system is active.
The Most Common Cause: Infection
The vast majority of swollen lymph nodes — particularly in children and young adults — are caused by localised infections near the affected node:
- Neck nodes: viral upper respiratory infections (colds, flu), strep throat, dental infections, ear infections, mononucleosis (EBV)
- Armpit nodes: skin infections or injuries on the arm/hand, breast infection, recent vaccination in the arm
- Groin nodes: leg or foot infections, sexually transmitted infections (chlamydia, syphilis, herpes), skin conditions
Reactive lymphadenopathy from infection typically resolves within 2–4 weeks as the infection clears.
Generalised Lymphadenopathy (Multiple Sites)
When lymph nodes swell in two or more non-adjacent regions simultaneously, this is called generalised lymphadenopathy and warrants investigation. Causes include:
- Mononucleosis (glandular fever) — classic in teenagers; EBV causes fever, sore throat, and widespread node swelling
- HIV infection (particularly acute/primary HIV)
- CMV, toxoplasmosis
- Autoimmune conditions: lupus, rheumatoid arthritis
- Drug reactions (phenytoin, allopurinol, sulfonamides)
- Lymphoma and leukaemia
Features That Raise Concern for Malignancy
Most swollen lymph nodes are not cancer — fewer than 1% of lymphadenopathy presentations in primary care turn out to be malignant. However, the following features significantly increase the likelihood of a serious cause:
- Persistence — nodes that have not reduced after 4–6 weeks
- Size — nodes >2 cm (roughly the size of a grape) are more concerning than smaller ones
- Firmness and fixation — hard, rubbery, or fixed (not mobile) nodes are more worrying than soft, tender, mobile ones (which suggest infection)
- No pain — lymphoma nodes are typically painless; infection nodes are usually tender
- Location — supraclavicular (above the collarbone) nodes are particularly suspicious regardless of size
- Associated B symptoms — unexplained fever, drenching night sweats, or ≥10% unexplained weight loss alongside node swelling strongly suggest lymphoma
- Age — in adults over 40, the risk of malignant causes increases
What to Do
If nodes are tender, appeared after a clear illness (sore throat, cold), and are reducing in size over 1–2 weeks — watchful waiting is appropriate. If nodes are enlarging, persistent beyond 4–6 weeks, painless, or accompanied by B symptoms or systemic illness, see your doctor. Investigation typically includes blood count with differential, ESR/CRP, monospot test, and chest X-ray. Biopsy may be needed if the cause remains unclear.