I have been having a hard time with wasswass, I have been obsessing over the ingredients in my skincare products and any products I’m using thinking that this product will make me najis and invalidate my prayer. I’ve read how if ingredients derived from animals go through a chemical change they’re tahir, but I don’t even know what that means. I don’t know how to differentiate if it has or hasn’t. Growing up I never thought twice about a lotion or chapstick, now I find myself analyzing every ingredient, scared to use it thinking it will invalidate my salah. Everything went from feeling easy to feeling extremely difficult, and I can’t tell if my concerns are justified and I should be avoiding these ingredients or if it’s just the shaytan trying to make deen hard for me. Please help me to understand if my concerns are valid or if I should ignore them and use my skincare freely amongst other things.

If you don’t know that there is any impure product in the lotion then you can assume it is pure.
There is no need to over-analyze it. Establishing whether something undergoes chemical change is not up to the scholar, it is established by an expert in that field who can verify that this change has actually occurred chemically.
Thus, unless you read the ingredients and see something that is a known impurity, then accept it as pure