With age and sun exposure, the skin's structural protein Collagen is damaged, leading to loss of skin firmness. The resulting loose or slack skin cannot support the compact structure around pores. So the pores relax and become visibly larger. Vitamin C can combat this process. It is an essential co-factor in the bio-production of Collagen. Thus, Vitamin C will increase Collagen, leading to firmer skin and smaller pores.
Another factor that contributes to larger pores is sebum, the skin's surface oil. Sebum is produced in the skin and flows onto the surface through the pores. Over time, the outward flow will expand the pore opening, leading to more visible pores. Vitamin B6 reduces the production of sebum. With less production, there is less outward flow of sebum through the pores, so the pore opening will shrink and become less visible.
Additionally, both Vitamin C and Vitamin E are anti-oxidants. Oxidation is involved in the process of skin damage from aging and sun exposure, such as damage to the structural protein Collagen. Thus, these two Vitamins protect the skin from oxidation and the subsequent increase in pore size.
This protective effect of Vitamins C and E is also important in other ways. Since oxidative damage to Collagen is involved in the formation of fine lines and wrinkles, preventing that damage with these anti-oxidant Vitamins will diminish the appearance of these skin problems. And since Vitamin C can increase Collagen production, it can both prevent oxidative damage and repair the existing damage to skin's structure.
Oxidation also impacts skin's sebum, the surface oil. These oxidized lipids can be irritating and cause blemishes, especially in those prone to acne. Vitamin C, in particular ascorbyl phosphate (which is the form of Vitamin C in Rebalance Vitamin C Serum), can protect against the oxidation of sebum and thus prevent breakouts. On top of that, Vitamin C is known to reduce the over-production of melanin, the skin's pigment found in age spots. Thus, it can diminish spots and improve skin color evenness. While it is tempting to suggest that oral Vitamin use might provide skin benefits, clinical testing in healthy subjects has not revealed any skin benefit from dietary use of Vitamins. There are several factors that may contribute to this lack of effect from oral use, such as metabolism of the Vitamin before it reaches the skin or insufficient concentration being achieved high up in the skin. The more effective approach is to apply the Vitamin in sufficient concentration directly to the area of the skin needing treatment.