Where is the line between "harmless dandruff" and pathological psoriasis?

The transitions are fluid. Cosmetic dandruff normally occurs over the entire surface of the scalp.

Dandruff flakes are somewhat larger with oily scalps and smaller with drier scalps.

Psoriasis symptoms

One of the signs of pathological psoriasis is when the skin is scaly over a very small area. The marginal areas of hair growth close to the ears and neck are frequently affected. Pronounced scaly, flaky skin can also often be found on other parts of the body (e.g. elbows / legs). A trip to the doctor can often be helpful as psoriasis is not a cosmetic problem.