X0306 4 2021-06-01 0 0001557746 Aclaris Therapeutics, Inc. ACRS 0001861790 Monahan Joseph C/O ACLARIS THERAPEUTICS, INC. 640 LEE ROAD, SUITE 200 WAYNE PA 19087 0 1 0 0 Chief Scientific Officer Common Stock 2021-06-01 4 M 0 50000 A 107132 D Common Stock 2021-06-02 4 S 0 18240 21.5039 D 88892 D Common Stock 2021-06-02 4 S 0 3550 22.3114 D 85342 D Common Stock 193 I By Spouse Restricted Stock Units 2021-06-01 4 M 0 50000 0.00 D Common Stock 50000 0 D Each restricted stock unit represents a contingent right to receive one share of common stock of the issuer. Shares sold to satisfy withholding tax obligations upon the delivery of shares of common stock for restricted stock units that vested on June 1, 2021 pursuant to preexisting sell-to-cover elections. The price reported is a weighted average sales price. The shares were sold in multiple transactions at prices ranging from $21.03 to $22.02, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The price reported is a weighted average sales price. The shares were sold in multiple transactions at prices ranging from $22.03 to $22.72, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer or the staff of the Securities Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The shares underlying these restricted stock units vested on June 1, 2021. /s/ Mark Ballantyne, Attorney-in-Fact 2021-06-02