X0306 4 2021-03-01 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 2021-03-01 4 M 0 17175 A 143821 D Common Stock 2021-03-01 4 F 0 4934 24.06 D 138887 D Common Stock 2021-03-02 4 M 0 6637 A 145524 D Common Stock 2021-03-02 4 F 0 1906 23.25 D 143618 D Employee Stock Option (Right to Buy) 24.06 2021-03-01 4 A 0 99500 0.00 A 2031-02-28 Common Stock 99500 99500 D Restricted stock units 2021-03-01 4 A 0 28400 0.00 A Common Stock 28400 28400 D Restricted stock units 2021-03-01 4 M 0 17175 0.00 D Common Stock 17175 34350 D Restricted stock units 2021-03-02 4 M 0 6637 0.00 D Common Stock 6637 19914 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. 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 four equal annual installments beginning on March 1, 2022, 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 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 2021-03-03