Certain Common Stock of Sienna Biopharmaceuticals, Inc. are subject to a Lock-Up Agreement Ending on 22-APR-2019. These Common Stock will be under lockup for 61 days starting from 20-FEB-2019 to 22-APR-2019. Details: The directors and executive officers, and largest stockholder have entered into lock-up agreements with the underwriters prior to the commencement of the offering pursuant to which each of these persons or entities, with limited exceptions, for a period of 60 days after the date of this prospectus supplement, may not, without the prior written consent of Cowen and Company, LLC and BMO Capital Markets Corp. on behalf of the underwriters offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any shares of common stock or any securities convertible into or exercisable or exchangeable for our common stock.