There is no real evidence that aloe vera (Aloe barbadenis) helps the skin in any significant way, but it’s not a throwaway ingredient. Some brands use aloe in place of water in their products, but aloe is actually 99.5% water.
There is research indicating that isolated components of aloe vera, such as glycoprotein, can have some effectiveness as a soothing agent. However, when mixed into a cosmetic product, it is doubtful that those qualities remain, although it may still play a role in binding moisture to skin. In pure form, aloe vera’s benefits on skin are probably its lack of occlusion and the refreshing sensation it provides. Aloe serves as a water-binding agent for skin due to its polysaccharide (complex carbohydrate) and sterol content. (An example of a sterol that’s beneficial for skin is cholesterol.) Although research has shown aloe also has soothing and antioxidant qualities, no study has proven it to be superior to other ingredients with similar properties, including such ingredients as vitamin C, green tea, pomegranate, and many other antioxidants.
References for this information:
Indian Journal of Dematology, 2008, issue 4, pages 163-166
Skin Research and Technology, November 2006, issue 4, pages 241-246
Journal of Ethnopharmacology, December 1999, pages 3-37