There are two ways people want to use store bought products in their DIYs. They’ll either want to add some concentrated DIY ingredients to a pre-existing product (for example, adding some hyaluronic acid to an otherwise complete moisturizer), or include some of a pre-existing ingredient in a recipe, often as an alternative for a concentrated DIY ingredient (for example, using a store bought hyaluronic acid serum instead of pure hyaluronic acid or a precisely made hyaluronic acid solution).
Store bought products are complete formulations. If they are an emulsion, the emulsifier will be carefully calculated to create a stable emulsion—as is. Adding additional ingredients can de-stabilize the emulsion, causing it to split.
If the product requires a preservative, that preservative system has been carefully designed and tested to preserve exactly that product. Adding additional ingredients can overwhelm or deactivate the preservative system, causing the product to spoil. Additional preservatives may conflict with the pre-existing one.
Store bought products containing a common ingredient (like a vitamin or extract) is very different from using the raw material. The raw material is always more concentrated, but you also know exactly how concentrated. Store bought serums rarely list their ingredients, but even if they do, trying to use a 5% serum in place of a 100% active won’t work well. You’d need to use 20x as much to get the same concentration of the active ingredient, and chances are there isn’t room in the formula for 20x more.
If you have a store bought product that sounds like it kinda-might-work, just use it the way it was intended to be and invest in the actual raw ingredient when you can.
Posted in: Safety