Skin will absorb a Vitamin C serum made with water faster, as up to 60% of the human body is made up of water. Water products also tend to have a lighter texture than those based with oil. This is due to water being less dense than oils.
However, when Vitamin C serums contain water, the potency and effectiveness of the Vitamin C ingredients vanishes. Poorly sourced ingredients, fillers, packaging, and water can all destroy the benefits of a Vitamin C serum over time. Water-based serums can start to degrade in as little as 3 months.
Most cheap Vitamin C serums are water-based and come in dark bottles. This is because Vitamin C is unstable and deteriorates once it is exposed to air or light.
In order to delay the deterioration of these water-based products, many serums will have added preservatives in their formulas. Many companies will advertise that "no harmful preservatives are added," but the face is sensitive, and it's best to aim for the most natural products.
An oil-based Vitamin C serum provides many benefits as it gives the skin an added layer of protection from harsh environmental pollutants. Having the right oils in your serum can help melt away the excess of build-up on your skin.
Vitamin C breaks down in water-based serums as quickly as 3 months, which is why many products that are water-based have preservatives. Oil-based products provide that extra level of protection that won't lead to the break down of the product.
An oil-based serum stabilizes the ingredients, ensuring they are potent and effective. This ensures that you will be getting moisturized and nourished skin without any harsh preservatives.