I took Aramis for his first vet visit, I told the vet about his skin scabs (crust) on his head and body. Turned out he had a skin infection.
The vet told me to use ketoclor  from Virbac. I had to wash him 3 times a week for 2 weeks.
The vet said I could wash  his whole body if I wanted; as he has a long coat I could only wash his belly and chest, the medication would make the skin infection go away anyway. So I did was him completely for the first week, and then washed only his belly and chest.
No more skin infection after the treatment.