I don't know *specifically* for psoriasis, but for any skin irritations - make sure to get plenty of essential fatty acids/ Omega3's in your diet (you could take flax oil, cod liver oil, fish oil, eat wild salmon or sardines, etc).
Stay very well hydrated.
Also stop using any harsh detergents or soaps. I read that goat's milk soap has a very close pH to human skin and is best. Definitely avoid SLS. Use jojoba oil (or another oil - like coconut oil - that is not petroleum based) on WET skin right out of the shower as a moisturizer. You want to seal in the moisture.
I usually get a bout of really dry skin when fall arrives and this system gets it back in shape.
Does psoriasis have a fungal element? I've forgotten - but if so make sure to treat that. I have a salve I use from a local herb store for fungal patches on the skin - you can check it out
here to see the ingredients and find something similar if that is needed. It works great! I warm it in my hand before I apply it and sometimes also add a couple drops of tea tree oil. (I have no affiliation with that store BTW - they just happen to be near me and I love their products and shop there regularly

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Good luck - I hope some of this is helpful
