This is a great question. As a general rule of thumb, skin care products are best applied from thinnest to thickest. For incorporating Retinol and Lytera 2.0 Skin Medica products, the following aesthetic skin care prescription is recommended: Step 1: In the AM and PM, begin your routine with a Skin Medica Facial Cleanser and Toner. Step 2: Next, apply corrective serums, like TNS Essential Serum, followed by Lytera 2.0, followed by Retinol (evening only). For TNS Essential Serum dispense on the back of hand and blend together before applying to skin. Apply to face, neck, and chest. For Lytera 2.0, product can be applied to entire face, neck, chest, or other affected areas. For Retinol, apply in the evening. If a Retinol product has never been used before, begin twice a week 2-3 days apart, increasing frequency slowly until daily use is tolerated. Mild redness, peeling and irritation is expected when using this product. Step 3: In the AM and PM, apply moisturizer, like Skin Medica Dermal Repair Cream. Apply a small amount all over the face and gently massage into the skin. Step 4: In the AM, apply a sunscreen, like TNS Total Defense + Repair. Be sure tp reapply every 2 hours if in direct sunlight and apply generously to face and other sun-exposed areas. Thank you for your question. Please be sure to consult with a board certified physician for all of your physician dispensed skin care needs.