As a child I had fairly severe psoriasis. I am 47 now and back then, the main treatments were steroid creams and cold tar ointment thankfully I went through puberty and it seem to disappear and I thought that was then end of it.
I was first diagnosed when I was 18. Psoriasis appeared over night literally! I went to bed after a night out absolutely fine and woke up in the morning covered in small scaly spots and patches all over my body, with no idea of what it was (never heard of psoriasis) my first GP thought it was chicken pox or scabies.