Retin-A and HRT is totally safe together, no interaction at all.
Retin-A will accelerate the normal changes of HRT by accelerating the turnover of the skin (so you get the male skin out quicker). It has much advantages on skin tones, but in your 20's you won't see that as much.
It works continuously to undo damage, even after 2 years, the base of the skin is still improving. The only problem, you've got to always put sunscreen on and carry it with you or you'll have a very bad sunburn (you have been warned) since it disactivate melanin's action when its used. After its stopped, melanin is reactivated within about 1 month.
Best thing is to use it conjonction with AHA's (lactic acid (like lac Hydrin) and glycolic acid daily (Neutrogena has a good PH balanced slow release 10% day cream) ).
