X0306 4 2019-02-01 0 0001557746 Aclaris Therapeutics, Inc. ACRS 0001654450 Ruffo Frank C/O ACLARIS THERAPEUTICS, INC. 640 LEE ROAD, SUITE 200 WAYNE PA 19087 0 1 0 0 Chief Financial Officer Common Stock 2019-02-01 4 M 0 3875 A 166284 D Common Stock 2019-02-01 4 F 0 1308 6.96 D 164976 D Restricted Stock Units 2019-02-01 4 M 0 3875 0.00 D Common Stock 3875 11625 D Restricted stock units convert into common stock on a one-for-one basis. The transaction reported represents the withholding of shares by the issuer to satisfy the reporting person's tax withholding obligations in connection with the vesting and settlement of the restricted stock units being reported in this Form 4. The shares underlying these restricted stock units vest in four equal annual installments beginning on February 1, 2019, subject to the reporting person's continuous service with the issuer as of the applicable vesting date. /s/ Mark Ballantyne, Attorney-in-fact 2019-02-05