Citric acid is an alpha hydroxy acid (AHA), derived from fruit and milk sugars. Its primary effect on the skin is that it causes mild exfoliation of the topmost layer of dead skin cells. Other than that, it is a powerful antioxidant, plays a role in skin-barrier function and has some astringent properties (which helps for the pore size to appear smaller).
As an ingredient on its own, it is beneficial for all skin types. However, it is especially so for acneic, hyperpigmented and/or aging skin for its following proven benefits:
-Promotes collagen synthesis
-Brightens dull skin tone
-Deals with dark spots, skin texture, etc.
-Firms the skin and gives it a more youthful appearance
…and much more.