Yes, you should apply the Obagi Professional-C Serum 15% followed by Obagi Nu-Derm Clear #3.

Obagi Professional-C Serum 15% is formulated with a pH of 2.0-2.4.

Yes, these two products can be used together in your routine. We recommend applying Obagi Professional-C Serum 15% as the first treatment step in your morning routine, followed by Obagi Nu-Derm Exfoderm #4. We hope this information helps!

Yes, you can use vitamin C and retinol together, as long as the vitamin C is applied in the morning and the retinol is applied at night. For best results, we recommend applying your products from the thinnest consistency to the thickest consistency.

Yes, storing your Obagi Professional-C Serum 15% (or any vitamin C serum) in the refrigerator can help slow down the oxidation process and potentially prolong the serum's effectiveness. Vitamin C (ascorbic acid) is known to be sensitive to light, air, and heat, which can cause it to oxidize and lose its potency over time. Oxidation leads to the serum becoming less effective, and in some cases, it may change color, turning brownish or yellow, which signals degradation. Storing in the Refrigerator: Slows Oxidation: The cool temperature of a refrigerator helps slow the breakdown of the vitamin C, maintaining its potency for a longer period. Prevents Heat Exposure: Heat accelerates oxidation, so keeping the serum in a cooler environment can protect it from this effect. Light Sensitivity: Vitamin C is also sensitive to light, so it’s important to store your serum in a dark place, whether that's in the fridge or in a drawer or cabinet away from direct sunlight. However, you should always keep the serum tightly sealed to prevent air from getting in, and avoid storing it in a place with excessive humidity (like near the fridge's freezer compartment) as this can also affect the product. Other Storage Tips: Keep it Upright: Store the serum upright to minimize air exposure to the formula. Close the Cap Tightly: Ensure the cap is tightly closed to avoid oxidation from air. While refrigeration can help prolong the shelf life of your Obagi Professional-C Serum, always monitor the serum for any changes in color, texture, or smell, which could indicate that it has already oxidized. If the serum turns dark brown or smells off, it's best to replace it. Let me know if you need more guidance!