At Peak Efficacy
Active ingredients are quite fragile and oxidize and degrade rapidly, even more so when repeatedly exposed to light, air, and touch. This is visible in Vitamin C solution which changes color from clear to brown over time. But it happens with many active ingredients - like vitamins, antioxidants, retinol, acids, and even oils - so much so that studies have shown the average skin care loses half its ingredient efficacy in just a few months! Not only are degraded ingredients ineffective, but some may also lead to skin sensitivity and irritation.