Since how long is the knot? Is there redness or visible swelling?
This seems to be mild grade of skin and underlying tissue inflammation (usually not related to the hormonal changes). An ice compress three to four times a day (around 10 minutes every time) with anti-inflammatory analgesics like Ibuprofen (Motrin or Advil), should take care of it.
If the symptoms aggravate (increase in swelling or tenderness/pain), he may need a course of antibiotics. That would need a visit to your primary care physician.
Please feel free for your follow up questions.
Would this be considered a swollen lymph node?
No, this is not the site for the lymph nodes, so would not be called swollen lymph node. It would be considered only mild grade skin or nipple tissue (ductal) inflammation / infection.
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