Scientific Name(s): Laccifer lacca
Common Name(s): Gommelaque, Lac, Lacca, Shellac
Shellac is the purified product of lac, the red, hardened secretion of the insect Laccifer (Tachardia) lacca Kerr. This tiny insect sucks the sap of selected trees and bushes, and secretes lac as a protective covering. The name lac is said to derive from lakh, the Sanskrit word for one hundred thousand, a reference to the very large number of insects involved in producing appreciable amounts of the product.1
Lac is cultivated in India, Thailand, and Burma. The whitest lac is produced by insects infesting the kusum tree (Schleichera trijuga). The harvester cuts twigs coated with lac into small pieces called sticklac. The crude material is ground and soaked in water to remove debris and insect bodies. The remaining material is soaked in sodium carbonate, which removes laccaic acid, a complex mixture of at least four structurally related pigments. The resulting granules retain the yellow pigment erythrolaccin and are dried to form seedlac. Further treatment by melting, evaporating, or filtering yields shellac.2
Shellac is most often used as a finish for fine furnitures. Further, the material has been used for almost 100 years by the pharmaceutical industry. Examples of shellac's role in this field include: Tablet coating formulations,3, 4, 5, 6 microencapsulation,7, 8, 9, 10, 11 matrix formation,12 enteric coating,13 humidity tolerance,14 and binding ability.15
Shellac has also been used as an ingredient in hair spray and in other cosmetics23, 24 However, shellac undergoes an aging effect upon storage and thus has fallen into disfavor as an ingredient in some preparations.2
The National Formulary XV recognizes 4 grades of shellac: Orange, dewaxed orange, regular bleached and refined wax-free bleached. The grades differ in the manner in which the seedlac is treated. Orange shellac is obtained by the evaporation of filtered ethanolic solutions of seedlac. It may be dewaxed by further filtration. Regular bleached shellac is obtained by dissolving the seedlac in aqueous sodium carbonate at a high temperature. After filtration, a bleaching agent (such as sodium hypochlorite) is added. The resin is removed by sulfuric acid precipitation. Refined wax-free bleached shellac adds another filtration step to remove the waxes.25
The exact chemical composition of shellac is unknown. It appears to be composed of a network of hydroxy fatty acid esters and sesquiterpene acid esters with a molecular weight of about 1000. Aleuretic acid, r-butolic acid, shellolic acid, and jalaric acid are the major constituents. The composition is a function of the source and time of harvest of the sticklac. Variability in the product may be a problem for commercial users of shellac. The physical properties of shellac also vary. For example, the reported melting point ranges from 77° to 120°C. Shellac is soluble in ethanol, methanol, glycols, glycol ethers, and alkaline water.1
Uses and Pharmacology
A 1-year prospective, randomized, controlled trial was conducted to determine the ability of shellac to prevent infection and progression of dry gangrene to wet gangrene in 26 patients with type 2 diabetes. The patients presented with peripheral dry, well-demarcated gangrene in their feet and were awaiting nonsurgical autoamputation because of contraindications to revascularization or surgery, limited life expectancy, and/or refusal of surgical amputation. Compared to conventional treatment with 10% povidone-iodine, the slightly lower rate of surgical amputation in the shellac group (46.2% vs 60%) was not statistically significant. None of the patients in the shellac group developed an allergic reaction.26
Research reveals no recent animal data regarding the use of shellac in a therapeutic application.
A randomized double-blind, controlled, clinical study evaluated the efficiency of shellac in reducing dentin hypersensitivity, which appeared to be as effective as the control agents tested.27
There is no clinical evidence to support specific doses of shellac for therapeutic purposes.
Pregnancy / Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking.
None well documented.
Allergy and contact dermatitis have been reported.28
Several cases of allergic contact dermatitis or eczema of the eyelids in women using mascara (Great Lash, Diorshow) have been documented with confirmed positive sensitivity to shellac through breakdown analysis of the product ingredients.29, 30
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