The last Vit C I used was La Roche Posay and it had 10% ascorbic acid. This is 15% so I am starting slow on dry clean skin.

Week 1: Once a week
Week 2: Twice a week
Week 3: Three times a week

Gradually moving up to everyday in the AM only

Week 1: Once a week for 1 week
Weeks 2 & 3: Twice a week for 2 weeks
Week 4 onwards: Three times a week, until the serum is finished.

Apply and wait 30 minutes before moving on to next step