Dandruff question. I have this hereditary thing but I can't remember what it is called! Any help???

So my father and I both have this dandruff thing. Its where you have a dry patch thats really itchy, and then when you scratch it, the spot gets like a sour in the middle of it. I use tea tree oil on it. My dermatologist told me the name of it but I cant remember. I know it either starts with an 'S' or 'C' and ends with 'sis'.