5ari like fin and dut inhibit the conversion of testosterone to DHT, meaning you have more testosterone. The more testosterone you have, the more estrogen you have, because testosterone is aromatised to estrogen.

Estrogen causes breast tissue to grow. Some men naturally almost have enough estrogen to cause them breast growth, either due to being an estrogen super-responder or already having a high estrogen level.

If they increase their estrogen level just a bit they will grow breast tissue.