Vitamin C E Ferulic and Layering Other Products

Regarding the stability of Vitamin C E Ferulic (L-Ascorbic Acid in a water base) compared to L-Ascorbic Acid in a silicone base when used with other products on the skin, the primary focus for stability is typically on the product's shelf life within its packaging (which can be 1-2 years), rather than the short period it is on the skin (30-60 minutes) when layered with other products.

While it's true that the characteristics of other products applied immediately after could theoretically affect the stability of Vitamin C on the skin (for example, if they have a high pH or contain heavy metal ions, which are generally undesirable in cosmetic formulations), this effect is usually less significant than the factors affecting the stability within the formula over months or years.

Vitamin C on the skin is already subject to degradation from the skin's natural pH (around 5.5), sunlight, and heat, even without other products being applied immediately after. The degradation during the short time it is on the skin before being absorbed or layered is generally not the main concern.

Regarding how long to wait after applying Vitamin C E Ferulic before applying other products, waiting about 30 minutes is a reasonable guideline. However, it's more important to consider whether the subsequent products are suitable for use with Vitamin C and if they might cause increased skin irritation, as Vitamin C itself is quite acidic.