Why understanding skin care ingredients is important?

Aside from general and somewhat impractical concept that one should know everything she ingests or applies to her body, there are specific reasons why the understanding of skin care ingredients is useful. In essence, a number of factors determine whether a topical skin care product has an antiaging effect:

• Do any of the ingredients have significant capacity to stimulate any aspects of skin regeneration, remodeling or renewal (e.g. collagen synthesis or cell turnover). In other words, are any of the ingredients active?
• Are active ingredients present in sufficient amounts and are they stable in the chemical environment of that particular formula? In other words, do active ingredients stay active during the typical shelf-life or do they degrade by reacting with air or other ingredients?
• Does the product's formula allow active ingredients to penetrate the skin well enough to be effective?
• Do any of the inactive ingredients interfere with the effect of the active ones? Do they have the potential to harm the skin, e. g. by causing allergic reactions, irritating or dehydrating the skin, clogging pores, etc.