Wikipedia states:
Ash Wednesday gets its name from the practice of placing ashes on the foreheads of the faithful as a sign of repentance. The ashes used are gathered after the Palm Crosses from the previous year’s Palm Sunday are burned. In the liturgical practice of some churches, the ashes are mixed with the Oil of the Catechumens[1] (one of the sacred oils used to anoint those about to be baptized), though some churches use ordinary oil. This paste is used by the minister who presides at the service to make the sign of the cross, first upon his or her own forehead and then on those of congregants. The minister recites the words: “Remember (O man) that you are dust, and to dust you shall return”, or “Repent, and believe the Gospel.”
and the Catholic Encyclopedia states:
Ash Wednesday
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The Wednesday after Quinquagesima Sunday, which is the first day of the Lenten fast.
The name dies cinerum (day of ashes) which it bears in the Roman Missal is found in the earliest existing copies of the Gregorian Sacramentary and probably dates from at least the eighth century. On this day all the faithful according to ancient custom are exhorted to approach the altar before the beginning of Mass, and there the priest, dipping his thumb into ashes previously blessed, marks the forehead – or in case of clerics upon the place of the tonsure – of each the sign of the cross, saying the words: “Remember man that thou art dust and unto dust thou shalt return.” The ashes used in this ceremony are made by burning the remains of the palms blessed on the Palm Sunday of the previous year. In the blessing of the ashes four prayers are used, all of them ancient. The ashes are sprinkled with holy water and fumigated with incense. The celebrant himself, be he bishop or cardinal, receives, either standing or seated, the ashes from some other priest, usually the highest in dignity of those present. In earlier ages a penitential procession often followed the rite of the distribution of the ashes, but this is not now prescribed.
There can be no doubt that the custom of distributing the ashes to all the faithful arose from a devotional imitation of the practice observed in the case of public penitents. But this devotional usage, the reception of a sacramental which is full of the symbolism of penance (cf. the cor contritum quasi cinis of the “Dies Irae”) is of earlier date than was formerly supposed. It is mentioned as of general observance for both clerics and faithful in the Synod of Beneventum, 1091 (Mansi, XX, 739), but nearly a hundred years earlier than this the Anglo-Saxon homilist Ælfric assumes that it applies to all classes of men. “We read”, he says,
Code:
in the books both in the Old Law and in the New that the men who repented of their sins bestrewed themselves with ashes and clothed their bodies with sackcloth. Now let us do this little at the beginning of our Lent that we strew ashes upon our heads to signify that we ought to repent of our sins during the Lenten fast.
And then he enforces this recommendation by the terrible example of a man who refused to go to church for the ashes on Ash Wednesday and who a few days after was accidentally killed in a boar hunt (Ælfric, Lives of Saints, ed. Skeat, I, 262-266). It is possible that the notion of penance which was suggested by the rite of Ash Wednesday was was reinforced by the figurative exclusion from the sacred mysteries symbolized by the hanging of the Lenten veil before the sanctuary. But on this and the practice of beginning the fast on Ash Wednesday see LENT.
Thanks for making me feel good 
Hey, my dad has cancer. Want to talk about that too? 
