What is the negative perception of chemically based Retin A? 

Sometimes they can be toxic and actually age skin in the long run by over thinning, stressing and over drying. In addition Retin A often contain warnings such as:
It is not known whether Retin-A will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant while using this medication.
It is not known whether Retin-A topical passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.