Dandruff is common thing in many individuals who at least experience once in their life time.. It's a normal exfoliation of skin. But some things do mimic common dandruff which require dermatologist Consulting to give proper treatment.

They are psoriasis which sometimes mimic dandruff but has discrete plaques on scalp or arms or elbows and knees

Times capitis which also mimics dandruff but has associated hair fall that needs to be treated with proper antifungal course.

Other conditions are discoid lupus which also shows scales like dandruff but associated with permanant hair fall..

identifying these conditions at the earliest stage rescues hair fall.