If you look closely on my scalp you can see flakes lying there.they get off very easly by scratch. sometimes my scalp looks red.no itch.what is this?

Dry skin, or scalp: seborrhea, which is basically dry skin. If you are on a medication, such as accutane, it could be exacerbated by that. You can try one of the dandruff shampoos on the market. If that doesn't help, ask your dermatologist to check and make a recommendation.

See your dermatologi: Assuming you see a dermatologist (or should be) taking these meds, they are all drying and irritating. It is unlikely she would advise all 3 at the same time. Also note that benzoyl peroxide bleaches fabrics and hair. Seborrheic dermatitis is NOT dry skin, but is a separate condition with different management. Review all this with your dermatologist so you can best manage it.