Common in newborns, presumably due to maternal hormones. Bud underneath the surface, plus swelling of areola/nipple area.
Another peak around puberty, can be unilateral, can be tender. Can progress to be cosmetically problematic.
Exclude a hormonal problem (including prolactinoma and other hormonal tumour):
- Delayed puberty with no development of penis/testes, no axillary/pubic hair
- Testicular mass