In my opinion, I don't believe there's any interaction between finasteride and psoriasis of the scalp. However, it's important to control the psoriasis if you are losing hair as it is an inflammatory process.PRPHAIRMD.COM
The use of Finasteride(Propecia) should not have any effect on scalp psoriasis.However,I would recommend having an evaluation by a Dermatologist.
This requires an in-person evaluation. I suggest seeing a hair loss expert now to evaluate and go over your condition and, if necessary, provide you information about your best treatment options. There are great non-invasive options like prp/progesterone and/or hair transplantation. See an expert. Best, Dr. Emer
Psoriasis is an inflammatory scalp condition. It is not mediated to any significant degree by DHT. Neither using or not using finasteride should affect a person's psoriasis.