I know that gelatin can be either from pigs or from cows, so it is better not to eat anything that has gelatin in it, especially since I am living in the U.S. But I heard that glycerin and glycerides are also Haram, is that really true? I remember seeing those two words in almost every thing I ate, and I thought that they were just chemical substances.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Dead animals, blood, the flesh of swine etc. are made forbidden as Allah Says in the Quran (what means): {Prohibited to you are dead animals, blood, the flesh of swine, and that which has been dedicated to other than Allah, and [those animals] killed by strangling or by a violent blow or by a head-long fall or by the goring of horns, and those from which a wild animal has eaten, except what you [are able to] slaughter [before its death], and those which are sacrificed on stone altars, and [prohibited is] that you seek decision through divining arrows. That is grave disobedience. This day those who disbelieve have despaired of [defeating] your religion; so fear them not, but fear Me. This day I have perfected for you your religion and completed My favor upon you and have approved for you Islam as religion. But whoever is forced by severe hunger with no inclination to sin - then indeed, Allah is Forgiving and Merciful.} [Quran 5:3]

In another Surah (Chapter) regarding this, Allah Says (what means): {Say, “I do not find within that which was revealed to me [anything] forbidden to one who would eat it unless it be a dead animal or blood spilled out or the flesh of swine - for indeed, it is impure - or it be [that slaughtered in] disobedience, dedicated to other than Allah. But whoever is forced [by necessity], neither desiring [it] nor transgressing [its limit], then indeed, your Lord is Forgiving and Merciful.”} [Quran 6:145]

In that manner, Allah forbade impure and harmful objects and made lawful every pure and useful object, as He mentioned this while reminding His favor on His Slaves by sending the Prophet Muhammad . Allah Says (what means): {…who enjoins upon them what is right and forbids them what is wrong and makes lawful for them the good things and prohibits for them the evil and relieves them of their burden and the shackles which were upon them.} [Quran 7:157]

Thereupon, you should recognize the ingredients of anything you want to use. Whatever contains any forbidden thing from the mentioned things, you should avoid it. And whatever does not contain that, then that is lawful and you may use it. If you had already used any forbidden thing, you should ask forgiveness from Allah. You are not supposed to pay any expiation except making repentance and asking pardon of Allah.

Allah knows best.