SNNA Sienna Biopharmaceuticals Inc

Sienna Biopharmaceuticals, Inc. (Nasdaq:SNNA), a clinical-stage biopharmaceutical company, today announced that it has elected to file a voluntary petition to allow restructuring under Chapter 11 of the Bankruptcy Code.

“We believe this decision is in the best interests of Sienna and its stakeholders,” said Frederick C. Beddingfield III, M.D., Ph.D., President and Chief Executive Officer of Sienna. “The protections afforded by Chapter 11 provide for an orderly restructuring process as well as additional time to pursue financial and strategic alternatives. Through this process, we expect to be able to maintain ongoing business activities while we continue to focus our resources on locating a purchaser or strategic partner to maximize the value of the Company.”

Sienna intends to continue to manage and operate its business under the jurisdiction of the Bankruptcy Court for the Distict of Delaware and in accordance with the applicable provisions of the Bankruptcy Code. Sienna has retained Latham & Watkins as legal counsel and Cowen and Company as its investment bank to review financial and strategic alternatives with the goal of maximizing stakeholder value.

About Sienna Biopharmaceuticals

Sienna Biopharmaceuticals, Inc. is a clinical-stage biopharmaceutical company focused on bringing unconventional scientific innovations to patients whose lives remain burdened by their disease. We draw upon our deep knowledge and experience in drug development across multiple therapeutic areas as we build a unique, diversified, multi-asset portfolio of therapies in immunology and inflammation that target select pathways in specific tissues, with our initial focus on one of the most important ‘immune’ tissues, the skin. We are leading the way with our novel proprietary technology platform, applying a scientific design process to create potent targeted pharmacologically active molecules that are directed toward a specific target tissue and a select disease pathway, and with minimal to no systemic exposure. At Sienna, we are going where it still matters for patients.

For more information, visit the Company’s website at www.SiennaBio.com.

Forward-Looking Statements

This press release contains forward-looking statements, including but not limited to statements regarding our belief that the voluntary petition under Chapter 11 of the Bankruptcy Code is in the best interests of Sienna and its stakeholders, our intent to maintain ongoing financing activities and collaborator obligations to to seek funding or partnerships that will allow us to advance our R&D pipeline, our intent to continue to manage and operate our business under the jurisdiction of the Bankruptcy Court. Such forward-looking statements involve substantial risks and uncertainties that could cause Sienna’s clinical development programs, future results, performance or achievements to differ significantly from those expressed or implied by the forward-looking statements. Such risks and uncertainties include, among others, Sienna’s need to raise substantial additional capital, uncertainties inherent in the pharmaceutical drug and medical device development processes, including regulatory approval processes, the timing of regulatory filings, the challenges associated with manufacturing pharmaceutical drug and medical device products, Sienna’s ability to successfully protect and defend its intellectual property, and Sienna’s ability to consumate a capital raising or other financial or strategic transaction. Sienna undertakes no obligation to update or revise any forward-looking statements. For a further description of the risks and uncertainties that could cause actual results to differ from those expressed in these forward-looking statements, as well as risks relating to the business of the Company in general, see Sienna’s most recent Annual Report on Form 10-K and any subsequent current and periodic reports filed with the Securities and Exchange Commission.

Contacts:

InvestorsIR@SiennaBio.com

Mediamedia@SiennaBio.com

Restructuring HotlineUnited States (Toll-free): 1-855-942-0397International: 1-503-597-7714