There are several reasons your scalp can be flaking.
Dandruff: Causes - MayoClinic.com
Dry skin. Simple dry skin — the kind you get during winter when the air is cold and rooms are overheated — is the most common cause of itchy, flaking dandruff. Flakes from dry skin are generally smaller and less oily than those from other causes of dandruff, and you'll likely have symptoms and signs of dry skin on other parts of the body, such as your legs and arms.
Irritated, oily skin (seborrheic dermatitis). This condition, one of the most frequent causes of dandruff, is marked by red, greasy skin covered with flaky white or yellow scales. Seborrheic dermatitis may affect not only your scalp, but also other areas rich in oil glands, such as your eyebrows, the sides of your nose and the backs of your ears, your breastbone, your groin area, and sometimes your armpits.
Not shampooing often enough. If you don't regularly wash your hair, oils and skin cells from your scalp can build up, causing dandruff.
Psoriasis. This skin disorder causes an accumulation of dead skin cells that form thick, silvery scales. Psoriasis commonly occurs on your knees, elbows and trunk, but it can also affect your scalp. It may be difficult to differentiate from seborrheic dermatitis if only the scalp is involved.
Eczema. If you have eczema anywhere on your body, it could also be on your scalp, possibly leading to the development of dandruff.
Sensitivity to hair care products (contact dermatitis). Sometimes sensitivities to certain ingredients in hair care products or hair dyes, especially paraphenylene diamine (PPD), can cause a red, itchy, scaling scalp. Shampooing too often or using too many styling products also may irritate your scalp, causing dandruff.
A yeast-like fungus (malassezia). Malassezia lives on the scalps of most healthy adults without causing problems. But sometimes it grows out of control, feeding on the oils secreted by your hair follicles. This can irritate the skin on your scalp and cause more skin cells to grow. The extra skin cells die and fall off, clumping with oil from your hair and scalp, making them appear white and flaky in your hair or on your clothes. Most often this eruption is identical to or closely resembles seborrheic dermatitis.
Exactly what causes an overgrowth of malassezia isn't known, although having too much oil on your scalp; changes in your hormones; stress; illness; neurological disorders, such as Parkinson's disease; a suppressed immune system; not shampooing often enough; and extra sensitivity to the malassezia fungus may contribute to the development of dandruff.
Sometimes dandruff doesn't respond to 1 shampoo. You need to try other types. I suggest keeping track of what products you try and how long you use it. Try rotating products also. Example use 1 for a couple days, then change to another. If you get no improvement, you should see a doc.
You want to learn the ingredients and choose a shampoo based on the active ingredient.
To protect your hair, saturate your hair with water, apply conditioner from the ends of your hair up towards the scalp. Leave about 1 inch conditioner free. Apply shampoo to the scalp and roots. Scrub with your finger pads until your arms want to fall off. Rinse.
Try Selsun Blue Dandruff Shampoo Deep Cleansing Micro-Bead Scrub
It contains 3% salicylic acid along with little beads that help to exfoliate.
Others to try.
Selsun Blue Dandruff Shampoo Itchy Dry Scalp contains Pyrithione Zinc - 1 %
Selsun Blue Medicated Maximum Strength Dandruff Shampoo contains Selenium Sulfide - 1 %
Hair Specific Problems: Hairline Breakouts, Static Electricity & Dry Scalp : Cosmetics Cop: Skin Care & Makeup Tips & Reviews
Dry, Flaky Scalp
A dry or flaky scalp could be caused by a variety of things. Changes in weather can affect scalp moisture and cause flaking. Winter produces a dry climate in houses, and the cold air outside can chap the skin. Overwashing in the summer from after swimming can also cause a change in the scalp. Some medications, such as isotretinoin, can cause surface dryness. Shampoos with strong detergent bases can dry out the scalp, as can plant extracts like peppermint or menthol.
The cause determines the course of action. If the products you're using are causing problems, stop! If you have to wash your hair frequently, don't lather more than once and try to massage the scalp as little as possible. If the environment in your house is a problem, put a humidifier in your bedroom, which can help the skin all over your body as well. If you still are struggling with a dry scalp and dandruff isn't the culprit (dandruff would not be affected by any of the things I'm suggesting), don't forget to massage a small amount of moisturizer into your scalp the night before you wash your hair.
Jojoba, coconut, avocado oil are all excellent and can be used to moisturize the scalp.
Adding a humidifier to your bedroom will add moisture back to the air which may help if the flakes are caused by dehydrated skin.