Sienna Biopharmaceuticals Engages Cowen to Explore Financial and Strategic Alternatives

Sienna Biopharmaceuticals, Inc. (Nasdaq:SNNA), a clinical-stage biopharmaceutical company, today announced that the Company has retained Cowen as an independent financial advisor to assist in exploring financial and strategic alternatives to maximize shareholder value. With Cowen's assistance, Sienna will continue to explore capital raising to enable the initiation of its planned Phase 3 pivotal clinical trials for SNA-120 (pegcantratinib), in addition to exploring a wide range of financial and strategic alternatives. Sienna does not intend to initiate its planned Phase 3 trials of SNA-120 until the Company secures sufficient additional capital.

No assurance can be given as to whether any particular financial or strategic alternative will be recommended or undertaken and, if so, upon what terms and conditions.

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 the potential of a capital raising transaction and the exploration of other financial and strategic alternatives. 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 consummate 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.

Contact:

InvestorsSean [e-mail]818-629-2244

MediaCaroline Van [e-mail]818-575-6250