I've had dandruff for about 3-4 years, but now i have a big red patch on my scalp, and small ones on my neck, and it's really itchy. what is this?

See dermatologist: This suggest that the cause for your dandruff is likely from a disease disorder or an allergic contact skin problem to agents used on area above the base of your neck. If you dye your hair (usually the black dye), the dye would be my first suspect. May try topical hydrocortisone in the meanwhile . See derm if problem persists.