Vitamin C actually has the opposite effect of making you more sun sensitive. Vitamin C protects the skin from free radical damage brought on by environmental aggressors (pollution, UV light, cigarette smoke, etc.) because it is an antioxidant. Given that vitamin C is such a strong antioxidant, it is frequently recommended for use during the day in addition to your SPF. This doesn't stop you from using vitamin C at night.
It's usually best to avoid layering these at the same time and slot ingredients known to cause sun sensitivity into your PM routine because vitamin C is acidic and doesn't always play well with other strong active(retinoids,peptides,AHAs, etc.) we recommend to use them separate times of the day to avoid any skin concerns.
Read More: What Does Vitamin C Do For Your Face?