Laundry detergent brands are not required to give you a list of ingredients. Most have Dodecyl benzene, saponins surfacants, solvent liquids, sodium phosphate, borax, and perfumes.
There is a lot of ingredients in Tide, many of which I cannot pronounce. I do not know what they are, but my best guess is that people are allergic to it because they have sensitive skin. There is one called Borax, and that just sounds scary to me.