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There are many websites which discuss symptoms, causes, and treatments for scalp psoriasis, and this is something I pulled from www.webmd.com/skin-problems-and.../psoriasis/scalp-psoriasis‎ 

Topical Treatments for Scalp Psoriasis

The first line of defense against scalp psoriasis is topical treatment: medicated shampoos, creams, gels, oils, ointments, and soaps. Although some of these products are available over the counter, stronger topical treatments require a prescription.

Over-the-counter products often contain one of two medications approved by the FDA for psoriasis:

Salicylic acid
Coal tar
Prescription products for scalp psoriasis may contain higher concentrations of salicylic acid, coal tar, or both, as well as other FDA-approved medications, such as:

Anathralin, an older prescription medication
Antimicrobials, which are used to treat bacterial or yeast infections associated with scalp psoriasis
Calcipotriene, a vitamin D derivative
Calcipotriene and betamethasone dipropionate (a potent steroid)
Other topical steroids
Tazarotene, a vitamin A derivative
To be effective, topical treatments must be applied to the scalp instead of just to the hair. They also must be used exactly as directed until you get adequate control of your lesions, a process that can take up to eight weeks or longer. After your psoriasis has cleared, you may be able to prevent recurrences by shampooing daily or twice-weekly with a shampoo containing coal tar or other medications.