Would like to know what is the difference between folliculitis decalvans and seborrheic dermatitis? i'm having an very dry itchy scalp. no scaling my scalp is sore with sores that scab up. there's no balding but the hair is thinning?

folliculitis is an inflammation of the root of the hair and can occur anywhere in the body. Seborrheic dermatitis is excess secretion of the sebum and occurs in areas where these glands are mores common on the skin E.G. the face and is oily and not dry. It is best that you see a dermatologist for prper management

Folliculitis decalvans is severe hair loss with scarring. This sounds more like seborrheic dermatitis. If a good dandruff shampoo like Selsun Blue or Head & Shoulders does not resolve the problem, see a dermatologist for a proper diagnosis and treatment.