Psoriosis Treatment How to quickly get effective Psoriosis relief

How does going to the tanning bed help psoriasis?

I have had psoriasis since I was 9. I'm 27 now. No medicines help. No creams or topical prescriptions help. It never goes away, but my dermotologist suggested going to the tanning bed. Just wondered if anyone knew "why" this helps or "how" it helps psoriasis.