Exhibit 32.1

CERTIFICATION PURSUANT TO

18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report on Form 10-Q of Sienna Biopharmaceuticals, Inc. (the “Company”) for the period ended March 31, 2019, as filed with the Securities and Exchange Commission on the date hereof (the “Report”), Frederick C. Beddingfield III, M.D., Ph.D., President and Chief Executive Officer of the Company, and Alexander Azoy, Chief Financial Officer of the Company, respectively, hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date: May 8, 2019	/s/ Frederick C. Beddingfield III
	Frederick C. Beddingfield III, M.D., Ph.D.
	President and Chief Executive Officer (Principal Executive Officer)
Date: May 8, 2019	/s/ Alexander Azoy
	Alexander Azoy
	Chief Financial Officer (Principal Financial Officer)