Lac resin, a natural secretion from the lac insect (Kerria lacca), has been used in various traditional medicine systems, particularly Ayurveda and Unani, for the treatment of external ulcerations. Historical texts describe its application as a protective covering or dressing for wounds and ulcers, taking advantage of its film-forming and adhesive properties. In these traditional contexts, lac resin is believed to promote healing, protect wounds from external contaminants, and perhaps provide mild antimicrobial effects due to certain minor bioactive compounds it contains.

However, there is a lack of robust scientific studies or clinical trials directly supporting the efficacy of lac resin for external ulcerations. While some in vitro research has looked at the antimicrobial or wound-healing properties of natural resins in general, lac resin has not been well studied in this context. The evidence, therefore, is primarily based on traditional usage and anecdotal reports, with minimal scientific validation. Its main role in wound care in folk medicine appears to be as a physical barrier rather than through any pharmacological action.

In summary, the use of lac resin for external ulcerations is rooted in traditional medicine practices, with little to no high-quality scientific evidence to confirm its efficacy for this indication.