Based on the reviews, the COSRX Vitamin C 13 Serum is best suited for individuals with combination skin, oily skin, and even sensitive skin. Many users with combination and oily skin types appreciated the lightweight and non-greasy texture, while those with sensitive skin noted that it was less irritating compared to higher concentration vitamin C products. However, it's important to note that some users with very sensitive skin did experience slight tingling or irritation, so it may be beneficial for sensitive skin users to start with a small amount and gradually increase usage.