Can I use this retinol serum in the morning, or is it only for nighttime?

This serum can be used in the morning, at night, or both — the directions recommend AM and/or PM application. That said, many retinol users prefer nighttime use because cell turnover naturally accelerates overnight, and because retinol increases sun sensitivity, which requires diligent SPF use during the day. If you do use it in the morning, applying a broad-spectrum sunscreen afterward is essential. For first-time retinol users, starting with nighttime-only application makes it easier to monitor how your skin responds before adding a morning step.