How to differentiate between psoriasis, dandruff and seborrheic dermatitis given that sd can sometimes be yellow?

See a doctor: Psoriasis causes cells to build up rapidly on the surface of the skin, forming thick silvery scales and itchy, dry, red patches that are sometimes painful.Dandruff is a common chronic scalp condition marked by itching and flaking of the skin on your scalp. Seborrheic dermatitis is a common skin disorder that mainly affects your scalp, causing scaly, itchy, red skin and stubborn dandruff.