i reckon its worth experimenting with lots of things untikl your find a good match for your needs.
Polytar has coal tar in so might smell a bit off, bt I aven't used it.
Some people find salt baths useful for plaue p, dead sea salts are popular, but I use Radox muscle saok bath salts myself.
Darrens right about the difference between plaque type and guttate type psoriasis, most emolients work best for very dry plaque type, so if your guttate is not dry, but just red pin pricks, you might be better including the salts, but I can't really say as I don't have guttate,
All my info about washing stuff can be found through this link -
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Logingood luck , brian