What's the primary cause of dandruff and itching?

Seborrhea: What you have is a condition known as seborrheic dermatitis a common, harmless, scaling rash affecting the face, scalp and other areas. It occurs most often where the skin is oily. Although it can be very persistent, treatment with regular use of antifungal agents and intermittent use of topical steroids can keep it under control. See a dermatologist for evaluation and treatment.