X0306 4 2017-12-15 0 0001557746 Aclaris Therapeutics, Inc. ACRS 0001604457 Walker Neal C/O ACLARIS THERAPEUTICS, INC. 101 LINDENWOOD DRIVE, SUITE 400 MALVERN PA 19355 1 1 0 0 President and CEO Common Stock 2017-12-15 4 M 0 3033 A 877052 D Common Stock 2017-12-15 4 F 0 922 24.23 D 876130 D Common Stock 2017-12-18 4 M 0 2925 A 879055 D Common Stock 2017-12-18 4 F 0 889 24.12 D 878166 D Restricted Stock Units 2017-12-15 4 M 0 3033 0.00 D Common Stock 3033 21233 D Restricted Stock Units 2017-12-18 4 M 0 2925 0.00 D Common Stock 2925 5850 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. On December 15, 2016, the reporting person was granted 24,266 restricted stock units, with 50% of the shares underlying the restricted stock units vesting in four equal annual installments beginning on December 15, 2017 and the other 50% of the shares underlying these restricted stock units vesting upon the achievement of a specified commercial milestone, subject to the reporting person's continuous service with the issuer as of the applicable vesting date. On December 18, 2015, the reporting person was granted 11,700 restricted stock units, vesting in four equal annual installments beginning on December 18, 2016, subject to the reporting person's continuous service with the issuer as of the applicable vesting date. /s/ Brian F. Leaf, Attorney-in-fact 2017-12-21