Less known facts about: Shellac

This article is part of the “Less Known Facts About Excipients” series by Philippe Tschopp.

Shellac Excipient: Origin, Enteric Chemistry, and Stability

Shellac is a natural polyester resin secreted by the female lac insect, and one of the few pharmaceutical excipients of insect origin. Its acid groups make it insoluble in gastric fluid and soluble at intestinal pH, which is why it remains one of the few naturally occurring options for gastro-resistant coating [1,6].

Where shellac comes from

Shellac is one of the few pharmaceutical excipients that is produced by an insect. Long before the development of modern enteric polymers, it was already being used to protect dosage forms from moisture and gastric acid, and it remains an important natural film former for pharmaceutical and nutraceutical applications [6]. It is a natural resin secreted by the female lac insect (Kerria lacca), which lives on specific host trees in India, Thailand, and other parts of Southeast Asia. The resin forms a protective coating around the insect colony and is harvested from the tree branches after the insects have completed their life cycle [6].

European regulators define the material in the same terms. In its 2024 re-evaluation, the EFSA Panel on Food Additives and Flavourings describes shellac as “the purified and bleached lac, the resinous secretion of the insect Laccifer (Tachardia) lacca Kerr (Fam. Coccidae)”, a taxonomic designation for the same species [1]. Both names appear across regulatory and supplier documentation for the excipient.

How pharmaceutical shellac is produced

The production process consists of several purification steps [6]:

• Lac insects colonize host trees such as Schleichera oleosa, Butea monosperma, and Ziziphus mauritiana, secreting a protective resin around the branches.
• Resin-coated branches, known as sticklac, are collected after the insects have matured.
• The sticklac is crushed, sieved, and washed to remove wood particles, insect residues, and natural impurities, producing seedlac.
• Seedlac is melted, filtered or solvent purified and converted into pharmaceutical-grade shellac with controlled purity, color, and wax content. Dewaxed grades are commonly used for pharmaceutical coating applications.

The decoloring step at the end of that sequence is not one process but two, and they do not produce the same material. EFSA distinguishes chemical bleaching, in which sodium hypochlorite oxidizes the pigments and introduces chloroform and organochlorine compounds, from physical decoloring, in which activated carbon removes the colorants and no chlorinated impurities are generated [1]. The distinction carries a regulatory consequence: the Panel derived an acceptable daily intake of 4 mg per kg body weight per day for wax-free shellac produced by physical decoloring, from a no-observed-adverse-effect level of 400 mg per kg body weight per day with an uncertainty factor of 100, while designating the ADI for chemically bleached shellac as temporary, pending toxicological data on the organochlorine impurities [1].

Wax content is likewise a specified quantity rather than a description. EFSA records two commercial grades, bleached shellac at not more than 5.5% wax and wax-free bleached shellac at not more than 0.2% wax [1]. USP-NF sets acid value and drying limits alongside these, with orange shellac at an acid value of 68 to 76 and the refined grade at 68 to 79, each at not more than 2.0% loss on drying [2].

What makes shellac chemically unusual

Shellac is a natural polyester resin composed primarily of hydroxy fatty acids and sesquiterpene acids [6]. EFSA describes the same architecture as “a complex mixture of different mono- and polyesters of hydroxyaliphatic acids and sesquiterpenoid acids”, with aleuritic acid among the primary components [1].

Its most valuable pharmaceutical characteristic is its pH-dependent solubility [6]:

• Insoluble in gastric acid
• Soluble under the more alkaline conditions of the intestine

This property allows shellac to function as a natural enteric coating material without requiring synthetic polymers [6]. In addition, shellac provides excellent moisture protection, good oxygen barrier properties, high gloss finishes, and good adhesion to tablets and pellets [6]. Moisture protection is assessed comparatively in film coating technologies for hygroscopic actives.

Where it is used in formulation

Pharmaceutical-grade shellac is used in enteric coatings, moisture barrier coatings, taste masking, modified-release formulations, pellet coatings, tablet polishing, and nutraceutical coatings [6]. Its primary functions include delaying drug release until intestinal pH, protecting moisture-sensitive APIs, improving product stability, and providing a natural coating alternative [6].

The nutraceutical and food side of that list rests on a separate authorization. Shellac is listed as E 904 and authorized as a glazing agent in the European Union, and the 2024 re-evaluation extended its permitted use to dietary foods for special medical purposes [1]. Colon-targeted work includes aqueous shellac ammonium salt films with inulin.

Considerations for formulators

As a natural material, shellac exhibits some batch-to-batch variability and its performance depends on the degree of purification, wax content, and aging. Pharmaceutical manufacturers therefore supply standardized grades with tightly controlled specifications [6]. Because shellac is insect-derived, it may not be suitable for vegan pharmaceutical or nutraceutical products. Formulators should also consider its relatively slow dissolution profile compared with modern synthetic enteric polymers such as methacrylate copolymers [6].

Aging is the item on that list with a documented mechanism. Shellac’s hydroxyl and carboxyl groups continue to self-esterify during storage, which lengthens disintegration time and, in aged films, can defeat dissolution at intestinal pH [3,4]. Reported fixes protect those carboxyl groups: converting shellac to a water-soluble salt, forming composite salts, or blending with hydrogen-bonding polymers. Limmatvapirat and colleagues, whose work the source newsletter cites, improved both the enteric properties and the stability of shellac films by forming composite salts with 2-amino-2-methyl-1-propanol and ammonium hydroxide, each salt compensating for the weakness of the other [3]. Shellac has also been combined with hydroxypropyl methylcellulose in controlled-release tablets.

The word “lac” originates from the Sanskrit “laksha”, meaning 100,000, a reference to the enormous number of lac insects required to produce commercial quantities of resin [6]. Although synthetic enteric polymers dominate many modern formulations, shellac remains one of the few naturally occurring excipients capable of providing gastro-resistant functionality [6].

This article is for informational purposes for pharmaceutical industry professionals and does not constitute regulatory advice. Always refer to the current pharmacopoeial monograph, the supplier’s current technical data sheet, and applicable regulatory guidance for your dosage form, route of administration, and market. Pharma Excipients International AG is not a manufacturer of the excipients discussed.

Sources

1. EFSA Panel on Food Additives and Flavourings (FAF), Younes M, et al. Re-evaluation of shellac (E 904) as a food additive and a new application on the extension of use of shellac (E 904) in dietary foods for special medical purposes. EFSA Journal, 2024;22(8):e8897. https://doi.org/10.2903/j.efsa.2024.8897
2. United States Pharmacopeia-National Formulary (USP-NF). Monograph: Shellac.
3. Limmatvapirat S, Limmatvapirat C, Puttipipatkhachorn S, Nuntanid J, Luangtana-Anan M. Enhanced enteric properties and stability of shellac films through composite salts formation. European Journal of Pharmaceutics and Biopharmaceutics, 2007;67(3):690-698. https://www.sciencedirect.com/science/article/abs/pii/S0939641107001476
4. Improvement of Bleached Shellac as Enteric Coating by Composite Formation. PubMed, 2021. https://pubmed.ncbi.nlm.nih.gov/34590171/
5. Rowe RC, Sheskey PJ, Quinn ME (Eds.). Handbook of Pharmaceutical Excipients. Pharmaceutical Press / American Pharmacists Association.
6. Source newsletter: Philippe Tschopp, “Less known facts about Excipients #2: Shellac,” LinkedIn newsletter, 2026. https://www.linkedin.com/pulse/less-known-facts-excipients-2-shellac-philippe-tschopp-shgxf/

Disclaimer

This article is based on publicly available information and industry sources at the time of writing and supported by AI. While every effort has been made to ensure accuracy, completeness, and fair representation, the author does not guarantee that all information is current, error-free, or reflective of the latest developments.

The content is provided for informational and educational purposes only and does not constitute technical, regulatory, or commercial advice. No liability is accepted for decisions made based on this material. Readers are encouraged to consult the original manufacturers and official sources to verify details before making professional or business decisions.

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