EXHIBIT A

AGREEMENT

Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, the undersigned hereby agree that only one statement containing the information required by Schedule 13G need be filed with respect to the ownership by each of the undersigned of Common Stock of Krystal Biotech, Inc.

Date: August 27, 2018	FRAZIER LIFE SCIENCES IX, L.P.
	By FHMLS IX, L.P., its general partner
	By FHMLS IX, L.L.C., its general partner
	By:	/s/ Steve R. Bailey
		Steve R. Bailey, Chief Financial Officer

Date: August 27, 2018	FHMLS IX, L.P.
	By FHMLS IX, L.L.C., its general partner
	By:	/s/ Steve R. Bailey
		Steve R. Bailey, Chief Financial Officer

Date: August 27, 2018	FHMLS IX, L.L.C.
	By:	/s/ Steve R. Bailey
		Steve R. Bailey, Chief Financial Officer

Date: August 27, 2018	By:	*
		James Topper

Date: August 27, 2018	By:	*
		Patrick Heron

Date: August 27, 2018	*By:	/s/ Steve R. Bailey
		Steve R. Bailey, as Attorney-in-Fact

This Agreement was executed by Steve R. Bailey on behalf of the individuals listed above pursuant to a Power of Attorney, a copy of which was filed with the SEC on July 31, 2017.