Ashes were imposed on the early catechumens when they began their preparation time for baptism. ... Other baptized Christians began asking to receive ashes in a manner similar to catechumens and penitents.

Is it a sin not to get ashes on Ash Wednesday?

No Rules, Just Right

Most (if not all) Catholics who attend Mass on Ash Wednesday choose to receive ashes, although there are no rules requiring that they do so. ... While most Catholics keep them on at least throughout Mass (if they receive them before or during Mass), a person could choose to rub them off immediately.

What is the response to receiving ashes?

Ashes Are Drawn on Foreheads

when the ashes are drawn on the forehead, the priest say one of these: “Remember, O man, that you are dust, and unto dust you shall return.” “Turn away from sin and be faithful to the Gospel.” “Repent, and hear the good news.”