DMAE, also known as dimethyl MEA, is a derivative of the B vitamin choline. It has been around for years as an oral supplement that's popularly believed to improve mental alertness, much like Ginkgo biloba and coenzyme Q10. However, the research about DMAE does not show the same positive results as the other two supplements.
Because DMAE is chemically similar to choline, DMAE is thought to stimulate production of acetylcholine. And because acetylcholine is a brain neurotransmitter, it's easy to see how it could be associated with brain function. However, only a handful of studies have looked at DMAE for that purpose and they have not been conclusive in the least, while some have shown that DMAE may be problematic or not very effective.
It’s a controversial ingredient for skin because research has shown conflicting results. It seems to offer an initial benefit that improves skin firmness, but these results are short-lived and eventually give way to destruction of the substances in skin that help keep it firm. DMAE may also have skin-calming effects.
Interestingly, there is a formulation challenge when including DMAE in skincare products. To maintain the efficacy and stability of DMAE, the product’s pH level must be at least 10. A pH of 10 is highly alkaline, which isn’t good news for skin.
Moreover, because almost all moisturizers (including serums and eye creams) are formulated with a pH that closely matches that of human skin (generally 5.5–6.5, which is on the acidic side of the scale), in all likelihood the DMAE included in skincare products cannot have any prolonged functionality.
References for this information:
Pharmazie, December 2009, pages 818-822
Journal of Drugs in Dermatology, Supplement 72, 2008, pages S17–S22
Aesthetic Plastic Surgery, November-December 2007, pages 711–718
British Journal of Dermatology, March 2007, pages 433-439
American Journal of Clinical Dermatology, Volume 6, 2005, pages 39–47
European Journal of Medical Research, May 2003, pages 183–191
Mechanisms of Aging and Development, February 1988, pages 129–138