As a skincare expert, I would recommend applying a ceramide serum before using retinol. Ceramides are lipids that help strengthen the skin's natural barrier, improve moisture retention, and protect against environmental damage. By applying a ceramide serum first, you can enhance the skin's barrier function, ensuring it is adequately hydrated and protected before introducing retinol.

Retinol, on the other hand, is a derivative of vitamin A and is known for its anti-aging benefits. It helps stimulate collagen production, reduce fine lines and wrinkles, and improve skin texture. However, retinol can be potentially irritating, especially for those with sensitive skin. By applying a ceramide serum beforehand, you can create a protective layer that minimizes potential irritation and helps maintain the skin's moisture levels.

So, to summarize, apply a ceramide serum first to nourish and strengthen the skin's barrier, followed by retinol to target specific concerns like aging. Remember to always patch test new products and consult with a dermatologist if you have any specific concerns or sensitivities.