Common side effects of hydroquinone include: Mild skin irritation and sensitization (burning, stinging)
What happens when hydroquinone stops working?
Continue prescribing hydroquinone for no more than four to five months. Allow the skin to rest and restore itself for two to three months after hydroquinone therapy. Resume hydroquinone therapy, if needed, only after such a break.
Can I use vitamin C while using Retin A?
If your skin care involves nothing but using vitamin C in the morning followed by nightly applications of Retin-A, youll have glowing, more youthful skin. (Sunscreen, of course, should also be applied daily.)
Is it OK to use vitamin C serum with Retin A?
In short: yes, you can use vitamin C and retinol together; try retinol at night and vitamin C during the day—always with sunscreen.