Apply CELIMAX Retinol Shot Tightening Serum only in the evening, on clean, dry skin, after cleansing and before your moisturizer. Start using it twice a week, then gradually increase if your skin tolerates it well. Use an amount equivalent to a small pea for the entire face, avoiding the eye and mouth areas. In the morning, be sure to apply sunscreen, as retinol makes the skin more sensitive to UV rays.