Research Stories

by Margaret Coulombe

Long used in spas as a beauty treatment, French green clay may have more power than people realize. ASU researchers are studying the antibacterial properties of this clay in the hopes that it may be used to heal as well as beautify (read the full story). Here is some more dirt on the stuff we call clay.

Attractive forces
Smectite is one of four major clay mineral groups. The others include illite, kaolinite, and chlorite. Each group has distinctive structural characteristics. These structural differences and the different elemental makeup of the clays affect the attractive or repulsive forces at the clay surface. As a result, each clay deposit has a unique character.

Clay can be found in a rainbow of hues. White, red, yellow, and green are most common. Green clays get their color from reduced iron. Smectite clays are the most often used in healing.

Rainbow of uses
Over time, clay has been used medicinally in every continent in the world—except maybe Antarctica. Clays have been implicated in cures for everything from acne to gangrene, cholera to goiters, antacids to arthritis, diarrhea to Buruli ulcer. The malleable nature of clay comes from its capacity to adsorb (ability to attract charged materials) or absorb (ability to pull up liquids like a sponge). Smectite is favored in personal care and for medical use. It is unique because it both adsorbs and absorbs.

Clay's absorptive capacity led to its early topical use in muds, astringents and cosmetics to draw up oils, secretions, and fluids from wounds. In ancient Greece, each of the Greek Isles was reputed to have special clay deposits, each with a different healing character. On Milos, the same pure white clay used in producing fine porcelains, paint, and white concrete was also baked into bread as a stomach aid.

In Lemnos, clay was mined and coins were "minted" that could be laid on the skin—to staunch bleeding, protect wounds, or draw away poisons or inflammation. Clay coins were minted worldwide into the 1800s. Modern French green clay, argile verte concassee, is prepared by washing, and then drying in the sun. Then it is milled to a fine powder, and sun dried a second time.

In modern pharmaceutical manufacturing, clays are used as lubricants (talc), emulsifiers, polar gels. and thickening agents. In cosmetics they are found in face masques, creams, powders, emulsions, and antiperspirants. And in spas, hot or cold, they can be mixed with water (geotherapy) or with sea water or mineral water, and then aged (pelotherapy), or combined with paraffin (paramuds).

Famous clay users include Cleopatra and Mahatma Gandhi.

To learn about research on the healing properties of clay, see "Healing clay."