The best time to apply vitamin C serum is generally in the morning after cleansing and toning, and before applying moisturizer and sunscreen. This timing allows vitamin C to provide antioxidant protection throughout the day against environmental stressors like UV rays and pollution. Applying it before sunscreen also boosts the effectiveness of sun protection. For people with sensitive skin, it might be better to apply vitamin C serum only at night to avoid irritation from sun exposure. Some people apply it both morning and night to maximize benefits, using it at night to support skin repair and rejuvenation while they sleep.

Here is a typical application sequence for morning:

• Cleanse the skin
• Tone
• Apply vitamin C serum
• Moisturize
• Apply sunscreen

At night, the serum is applied after cleansing and toning, followed by moisturizer or night cream to enhance skin repair.

In summary, morning use is recommended for protection and daytime benefits, with night use optional for enhanced repair, depending on skin sensitivity and personal preference.