The Use of the Grape in Glycolic Acid

Unripe grapes

Glycolic acid (α-hydroxyacetic acid) has the chemical structure HO-CH₂-COOH.
Alpha-hydroxyacetic acid is used in skin care products. It reduces wrinkles and improves other skin conditions. Glycolic acid monomer is used to prepare polyglycolic acid, from which dissolvable sutures are manufactured. Sources of glycolic acid include fruits and vegetables high in sugar content, including green (unripe) grapes.

Chemical & Physiologic Properties

Glycolic acid is the simplest of the alpha-hydroxy acids. It consists of odorless white, hygroscopic crystals. Because of its small molecular weight and size it affords strong skin penetration. Alpha-hydroxy acids loosen glue-like substances that hold surface skin cells together. Because of this, treatment softens the skin.

Preparation From Natural Sources

Although glycolic acid can be produced from unripe grapes, fermented sugar cane juice is a more common source. Additional sources include barley and wheat leaves, cantaloupe, sugar beets and pineapple. Chemical methods of production are being used by some manufacturers such as DuPont.

Chemical Preparation

One patented chemical preparation of particularly pure glycolic acid involves the saponification of chloroacetic acid with an excess of alkali metal hydroxide, later followed by electrodialysis. The overall reaction is

ClCH₂-COOH + M⁺OH⁻ ' HOCH₂-COOH +M⁺Cl⁻,

where the metal ion, M⁺ is typically sodium, Na⁺, or potassium, K⁺.

Cosmetic Skin Peels

Facial peels (superficially thin) using 40 percent to 70 percent glycolic acid improve skin texture, facial lines and mottled pigmentation. Kits for home use are considerably weaker. Treatment consists of a series of peels over a period of weeks. Two-minute time exposures to the acid are typical, though the reaction can be halted at any time by treatment with neutralizer.

Advisories

The Food and Drug Administration offers "guidance for industry" concerning increased sunburn risks for people using glycolic acid for cosmetic purposes.
Glycolic acid metabolizes to form oxalic acid, hence ingestion is hazardous; however, in cases of ingestion, vomiting should not be induced. Material Safety Data Sheets list glycolic acid as a corrosive solid, capable of causing severe irritation and burns. It also represents an inhalation hazard.

References

• CrossChem: "Glycolic Acid" (Enzymatic Preparation)
• Johns Hopkins Cosmetic Center: "Glycolic Acid Peels"
• FDA: "Labeling for Topically Applied Cosmetic Products Containing Alpha Hydroxy Acids..."

Resources

• US Patent 5723662 -- "Process for preparing a particularly pure glycolic acid"
• Just Answer Medical: 'Glycolic Acid Ingestion'
• DuPont: "Glycolic Acid"