As someone who suffers from allergies to several common chemical ingredients myself, I cannot stress this enough: if you suspect you are hypersensitive, please do not diagnose yourself. Visit your physician, they will know how to diagnose your condition. Maybe you have a migraine triggered by some odors? Maybe you have Neurodermatitis? Maybe it is just "normal" dermatitis?
As far as the correlation between price and ingredient quality, I can say this from experience: synthetic surfactants are cheaper than either animal fat or natural (plant) oil-based surfactants. Which kind is best depends on your skin. Furthermore, the more higher the water content in a cosmetic product, the higher the preservative requirements. At any rate, the INCI list is a better indicator of what you are looking after compared to retail price, as already mentioned.
There is no "generally good" or "generally bad" ingredient as long as FDA (or EUPH)-approved. I will try an analogy: there is much speculation about aluminum's impact on health. The fact is, as of the time point of writing, nobody has proved causality of neurological diseases by aluminum. Maybe Alzheimers causes a high aluminum content in the brain and not vice versa?
As far as the correlation between price and ingredient quality, I can say this from experience: synthetic surfactants are cheaper than either animal fat or natural (plant) oil-based surfactants. Which kind is best depends on your skin. Furthermore, the more higher the water content in a cosmetic product, the higher the preservative requirements. At any rate, the INCI list is a better indicator of what you are looking after compared to retail price, as already mentioned.
There is no "generally good" or "generally bad" ingredient as long as FDA (or EUPH)-approved. I will try an analogy: there is much speculation about aluminum's impact on health. The fact is, as of the time point of writing, nobody has proved causality of neurological diseases by aluminum. Maybe Alzheimers causes a high aluminum content in the brain and not vice versa?