LESSON 4 · Skin Science
The Single Most Important Product
If you could only use one skincare product for the rest of your life, every dermatologist on earth would tell you to choose sunscreen.

That expensive retinol, vitamin C serum, and moisturizer you use? They are fighting damage that sunscreen would have prevented in the first place. Prevention is always cheaper and more effective than repair. Yet sunscreen remains the most skipped step in most routines.