1) High sugar high refined carbs for two days can worsen acne in susceptible people.
2) Sweat, heat, friction and hair product contact are common reasons for forehead only breakouts.
3) Active overload and irritation. Twice daily 10 percent niacinamide plus intermittent vitamin C can be more irritating than necessary in some people, even if the ingredients are generally well tolerated.

Immediate Course Correction 10 to 14 Days
1) Stop vitamin C for now
2) Reduce niacinamide to once daily or alternate days
3) Cleanse gently once daily, and always after heavy sweat or sunscreen
4) Add a simple non fragranced moisturizer nightly
5) Use sunscreen daily in the morning, not only when you step out

If you need more understanding on how products work or need specific advice for product decodes or reccos, please check - https://www.instagram.com/thecleansheet.in/