X0306 4 2020-03-02 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 2020-03-02 4 M 0 17175 A 103978 D Common Stock 2020-03-02 4 F 0 4779 1.26 D 99199 D Restricted stock units 2020-03-02 4 M 0 17175 0.00 D Common Stock 17175 51525 D Employee Stock Option (Right to Buy) 1.26 2020-03-02 4 A 0 92928 0.00 A 2030-03-01 Common Stock 92928 92928 D Restricted stock units 2020-03-02 4 A 0 66377 0.00 A Common Stock 66377 66377 D Restricted stock units 2020-03-02 4 A 0 26551 0.00 A Common Stock 26551 26551 D Each restricted stock unit represents a contingent right to receive one share of common stock of the issuer. 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 March 1, 2020, subject to the Reporting Person's continuous service with the issuer as of the applicable vesting date. Exercisable with respect to 25% of the shares subject to the option vesting on each of the first, second, third and fourth anniversaries of the grant date, subject to Reporting Person's continuous service through each such date. The shares underlying these restricted stock units vest in two equal annual installments beginning on June 1, 2020, subject to the Reporting Person's continuous service with the issuer as of the applicable vesting date. The shares underlying these restricted stock units vest in four equal annual installments beginning on March 2, 2021, subject to the Reporting Person's continuous service with the issuer as of the applicable vesting date. /s/ Mark Ballantyne, Attorney-in-fact 2020-03-04