Glycolic acid (or hydroxyacetic acid) is the smallest alpha-hydroxy acid (AHA). This colourless, odourless, and hygroscopic crystalline solid is highly soluble in water. Due to its excellent capability to penetrate skin, glycolic acid is often used in skin care products, most often as a chemical peel. It may reduce wrinkles, acne scarring, and hyperpigmentation and improve many other skin conditions, including actinic keratosis, hyperkeratosis, and seborrheic keratosis. Once applied, glycolic acid reacts with the upper layer of the epidermis, weakening the binding properties of the lipids that hold the dead skin cells together. This allows the outer skin to dissolve, revealing the underlying skin. It is thought that this is due to the reduction of calcium ion concentrations in the epidermis and the removal of calcium ions from cell adhesions, leading to desquamation. Glycolic acid is a known inhibitor of tyrosinase. This can suppress melanin formation and lead to a lightening of skin colour. Acute doses of glycolic acid on skin or eyes leads to local effects that are typical of a strong acid (e.g. dermal and eye irritation). Glycolate is a nephrotoxin if consumed orally. A nephrotoxin is a compound that causes damage to the kidney and kidney tissues. Glycolic acid's renal toxicity is due to its metabolism to oxalic acid. Glycolic and oxalic acid, along with excess lactic acid, are responsible for the anion gap metabolic acidosis. Oxalic acid readily precipitates with calcium to form insoluble calcium oxalate crystals. Renal tissue injury is caused by widespread deposition of oxalate crystals and the toxic effects of glycolic acid. Glycolic acid does exhibit some inhalation toxicity and can cause respiratory, thymus, and liver damage if present in very high levels over long periods of time. Elevated glycolic acid without elevated oxalic acid is most likely a result of GI yeast overgrowth (Aspergillus, Penicillium, probably Candida) or due to dietary sources containing glycerol (glycerine). (http://drweyrich.weyrich.com/labs/oat.html). Glycolic acid has also been found to be a metabolite in Acetobacter, Acidithiobacillus, Alcaligenes, Corynebacterium, Cryptococcus, Escherichia, Gluconobacter, Kluyveromyces, Leptospirillum, Pichia, Rhodococcus, Rhodotorula and Saccharomyces (PMID: 11758919; PMID: 26360870; PMID: 14390024).