Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
These concerns usually need timely assessment but are not automatically emergencies.
Call emergency services for severe breathing difficulty, sudden chest pain, fainting, confusion, or bleeding that will not stop.
These are not typical early signs of Paget's disease but may signal a serious treatment complication or another emergency.
Arrange a medical appointment promptly if you have a nipple rash, crusting, discharge, flattening, or soreness that is new, affects one side, or does not settle.
You should also be assessed for a new breast lump or thickening.
These symptoms have many possible causes and are often not due to cancer.
However, persistent one-sided nipple changes need examination.
Do not repeatedly treat them as eczema without medical review.
Seek urgent medical care for a surgical wound that becomes increasingly red, hot, swollen, or painful, especially with fever or pus.
The article also says
If you have already been treated, contact your care team about a new breast or chest-wall change, swelling of the arm, persistent bone pain, unexplained weight loss, or a new symptom that does not improve.
Every sign above is quoted from the sofidex article on Mammary paget's disease. If you are not sure, err upward — it is always reasonable to be checked.