It seems that you have a rather severe case of dandruff. Do not scratch your scalp as this will only aggravate your condition. By itself dandruff does not cause hair fall but scratching your scalp vigorously can damage the roots of your hair causing undue hair fall. Your scalp is home to various bacteria and fungi. However, in some people there is an excess of a certain type of scalp specific fungus (P. ovale), and this causes excess flaking.
Make sure that you have a healthy diet that is rich in B-complex, zinc and proteins. Stress and pollution can also aggravate your condition. Make sure that you wash your hair regularly. Since your dandruff is severe, I suggest that you first use a shampoo that contains Ketoconazole. Ketoconazole kills the fungus that causes dandruff and therefore it can completely cure your problem for good. Once your dandruff is under control, I suggest that you use a few natural remedies to keep dandruff at bay.
If you have dry hair using a shampoo meant for oily hair can dry your scalp and leave your hair dry and limp. It is therefore important that you only use shampoos and hair products that are meant for your specific hair type. Try to use an egg conditioner at least once a week. You can mix honey, egg yolk and a few drops of lemon juice and use this mixture to slowly massage your scalp. Leave it on for at least 30 minutes before washing it off with lukewarm water. If you dislike the slight lingering smell (due to the egg yolk) you can use black gram flour instead. I would suggest that you steam your hair at least once a month. Steam allows the oil to be easily absorbed by the hair follicle itself and this increases its effectiveness.
answered by G R