I've been a long-time observer and have wanted to bring this up for a long time but wasn't sure if this topic was allowed or not. Please let me know if this violates any rules and I will happily delete. This question is simply for the sake of discussion and is something that's been rolling around in my own head for a while now. I own a small skin care company and my family owns a biotech lab that specializes in the functionalization of nanodiamonds and so this conversation always comes up.
The increase in nano materials in cosmetics seems to be creating a fine line between cosmetic products and transdermal drug delivery masked as cosmetics. Any substance that penetrates the dermis or affects skin metabolism is considered a drug (assuming no drug claims are made, etc). But where does the line exist with nano 'carriers' (liposomes, nanosomes, nanocapsules, nanodiamonds, etc) of cosmetic ingredients, which have the potential to amplify ingredient efficacy, deliver ingredients into deeper skin layers and target specific sites based on ph, temperature etc? For example, functionalizing the surface of a nanodiamond with HA could deliver the ingredient deeper into the skin's surface, making it more biologically active, or, due to the massive surface area of nanoparticles, they could also magnify the efficacy of salicylic acid or retinol while remaining within cosmetic limits. It has also been shown that certain ingredients can 'unwind' from nanocarreirs based on wound/acne based on ph, resulting in targeted, sustained delivery and the creation of ingredient 'reservoirs' at the site (again, potentially overcoming the limitations of allowable concentrations in cosmetics).
While it is debatable whether some nanoparticles actually penetrate the skin, it's been proven that specific nano carriers are effective transdermal delivery vehicles and lack of peer reviewed product-specific studies hasn't stopped some companies from making claims that resemble transdermal delivery. For example, Loreal uses nanosomes of pro-Retinol A and makes the claim "enriched with fortified Pro-Retinol A®, penetrates the skin’s surface to effectively fight wrinkles and reduce the appearance of neck creases." Does the 'penetration' of the skin's surface through the use of nanosomes (which is debatable in reality) classify it as a drug? Or is it considered a cosmetic if it hasn't been proven to enter the blood stream? Either way, it raises the question: Does delivery mechanism impact whether a cosmetic is no longer considered a cosmetic, but a drug?
Nanodiamond–insulin complexes as pH-dependent protein delivery vehicles: https://www.researchgate.net/profile/Xiaoyang_Xu4/publication/26698662_Nanodiamond-insulin_complexes_as_pH-dependent_protein_delivery_vehicles/links/5728b5a408aef7c7e2c0c158.pdf
Comprehensive evaluation of carboxylated nano diamond as topical drug delivery system:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4887070/