What are probable causes of slightly swollen lymph nodes around the neck?

Infection... The most common cause of slightly swollen lymph nodes around the neck are infections caused by viruses and bacteria. Upper respiratory infections, mononucleosis, and strep throat are common infectious agents. After the infection is cleared by the body, the swollen lymph nodes can sometimes take 1-2 months to subside. Much rarer causes are cancers like lymphoma.