Bentonite clay
Bentonite clay is one of the most common forms of clay used in topical skin products. Bentonite clay, formed after volcanic ash has weathered and aged in the presence of water, is named after a formation called Benton Shale in the western United States. Bentonite has a strong negative electromagnetic charge and when mixed with water it swells like a sponge and can absorb 40-50 times its weight.
There are several types of Bentonite clay, named from the dominant element found within: Sodium bentonite, calcium bentonite, aluminum bentonite, and potassium bentonite are the most common. Bentonite clay is most commonly found in off-white or green colors.
Kaolin and red clay
Typically white or nearly white to sometimes gray in color, kaolin clay is one of the other most common types of clay used in skin care. While the minerals of the kaolin group display a relatively small specific surface area, compared with those of other clay groups, they can still adsorb small molecules, proteins, bacteria, and viruses on the surface of their particles.
Red clay, also sometimes seen in skin care, takes on its color because of a higher content of iron oxides.
In a 2011 study, Valenti et al. evaluated the impact of daily application of clay and retinoic acid 0.025% on the skin of rats.After 7 days, skin where clay had been applied showed a significant increase in collagen fibers, compared with control skin, while areas where retinoic acid had been applied did not show a significant increase in collagen fibers, compared with control skin.2
A recently published study claims that pH and its interaction with the clay particle surface charge may neutralize and impact properties – including antibacterial properties – of clay and is more significant than previously thought.3 The authors emphasize the dangers of this possibility with unregulated marketing and unsubstantiated bioceutical claims of products that contain clay. Many clay-based skin care products on the market today include other ingredients such as acids (for example salicylic acid, lactic acid, and malic acid) that may potentially counteract this issue and help enhance the targeted efficacy of the product.
The types and characteristics of all types of clay go beyond the scope of this column, but as demonstrated throughout history, clay may have a role in medicinal and dermatologic care, the research of which is still ongoing and is important in our understanding of how this earthly compound can affect our bodies.
Dr. Wesley and Dr. Talakoub are cocontributors to this column. Dr. Wesley practices dermatology in Beverly Hills, Calif. Dr. Talakoub is in private practice in McLean, Va. This month’s column is by Dr. Wesley. Write to them at dermnews@mdedge.com. They had no relevant disclosures.
References
1: Moraes JDD et al. Int J Pharm. 2017 Dec 20;534(1-2):213-219. doi: 10.1016/j.ijpharm.2017.10.031.
2: Valenti DMZ et al. Clin Exp Dermatol. 2012 Mar;37(2):164-8. doi: 10.1111/j.1365-2230.2011.04216.x
3. Incledion A et al. Biomolecules. 2021 Jan 5;11(1):58. doi: 10.3390/biom11010058.