Is it possible to have psoriasis on your head. If so how do you treat?

Sure. The scalp is one of the most common areas of involvement for psoriasis; some people have it only on the scalp. First line of treatment is one of the stronger therapeutic shampoos containing tar, salicylic acid, zinc pyrithione, or selenium sulfide. (keep it out of your eyes.) if that doesn't get it done, you'll need to see a dermatologist and get a prescription strength shampoo, lotion, or both.