1.Vitamin A and its derivatives need to be converted into retinoic acid (except HPR) to be effective.

2.Retinol causes skin irritation through mechanisms including stimulation of TRPV1 receptors, upregulation of AQP3 expression, disruption of desmosomes, and affecting the expression of barrier-related structural proteins.

3.Products containing retinol and its derivatives are best used at night with proper hydration and moisturization beforehand. If used during the day, diligent sun protection is essential. Gradual introduction helps build skin tolerance to retinol.