X0306 4 2018-05-07 0 0001557746 Aclaris Therapeutics, Inc. ACRS 0001654337 Ali-Jackson Kamil C/O ACLARIS THERAPEUTICS, INC. 640 LEE ROAD, SUITE 200 WAYNE PA 19087 0 1 0 0 Chief Legal Officer Common Stock 2018-05-07 4 M 0 6933 A 94610 D Common Stock 2018-05-07 4 F 0 1974 18.10 D 92636 D Restricted Stock Units 2018-05-07 4 M 0 6933 0.00 D Common Stock 6933 5200 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 13,866 restricted stock units. 50% of the shares underlying these restricted stock units vested on May 7, 2018 upon the achievement of a specified commercial milestone. The other 50% of the shares underlying the restricted stock units vest in four equal annual installments beginning on December 15, 2017, subject to the reporting person's continuous service with the issuer as of the applicable vesting date. /s/ Brian F. Leaf, Attorney-in-fact 2018-05-09