Can your skin get used to retinol so that it becomes less effective?
Your skin gets used to the side effects of retinol, such as flaking and redness, but not to the effect itself; the active effect on lines and pigmentation does not diminish with longer use.
Your skin gets used to the side effects of retinol, not to the effect itself. That is an important distinction. In a 10-week study using retinol 0.5%, participants experienced flaking and redness in the early stages. By the end of the study, those complaints had largely disappeared, while the product continued to work just as well.
The fact that its efficacy does not diminish with longer use is confirmed by multiple studies, including an analysis of 23 randomised trials. In those trials, continued use of retinol significantly improved fine lines and uneven pigmentation. None of those studies reported that the effect weakened over time.
The phenomenon whereby a product becomes less effective because the skin gets used to it has simply not been described for retinol in the available literature. Long-term safety and efficacy are, in fact, rated positively.
One caveat: retinol is less potent than prescription variants such as tretinoin or tazarotene. Those work more powerfully, but also cause more irritation. If after a while you feel that retinol is doing less, that may be due to the concentration or the product, not to tolerance.
Based on one open-label study (10 weeks, retinol 0.5%), a network meta-analysis of 23 RCTs, and multiple additional studies into the long-term efficacy and tolerability of retinol.