Most cases of an itchy scalp are caused due to a case of fungus of the scalp. The fungus that causes this scalp is closely related to the yeast family that is responsible for tinea versicolor and the same fungus is also implicated in seborrheic dermatitis. Since you didn't mention that you are experiencing flaking of the skin, this probably means that your oil secretions are still adequate to trap dead skin cells or yours is not a very severe case of dandruff. Treating dandruff is quite simple; all that you need to do is to get rid of the fungus. There are a number of shampoos that are topical medications which will help you. Added to this some simple home remedies and you should be rid of the problem. Note however, that the problem can recur if the fungus comes back; at which point, you should resume the same regimen.
When the malessezia globosa fungus starts to proliferate in large numbers on the scalp, the skin starts to get irritated and the top most layer of the skin starts to undergo massive cell death. This results in dead skin cells being shed. This process occurs normally also but the cell turnover rate is almost double in the case of dandruff. The fungus feeds on deposits of fat and oil from the skin secretion, sebum. Sebum is rich in triglycerides, wax monoesters, and essential fatty acids. Since the malessezia fungus monopolizes all the sebum on the scalp, the dead skin cells will fall off as white flakes copiously.
Treating dandruff and an itchy scalp is rather simple and all you need to do is to start using an anti-dandruff shampoo that contains either ketoconazole, selenium sulfide, or zinc pyrithione. These are all substances that are cytotoxic to fungi. Additionally, you need to use some tea tree oil on your scalp as this is an antibacterial and antifungal agent. Every now and then, it would be a good idea to wash your hair and scalp with hydrogen peroxide. This substance is also cytotoxic to fungal cells. Dandruff can take some time to treat and you might have to end up waiting a whole month sometimes before the condition is completely eliminated. However, your itching will stop as soon as you use the hydrogen peroxide. In time you should limit the use of hydrogen peroxide because it can end up causing a bleaching effect in your hair. For this reason, you should also dilute it slightly with water before using it.
answered by G M