Ok, here is what I recommend for Dry Itchy Scalp, it's called Dandrene and it's made by DS-Labratories. They are the premiere line of scalp solutions on the market and the price is great too, $28.00 for a 3 month supply. They advertise themselves as ultra premium formula to target the symptoms of seborrhic dermatitis. You will achieve best results with the potent mix of modern science and botanical extracts.
Directions: This is how you will get the best results from both shampoo and conditioner of any kind. Wet your hands, squeeze product into palm, then (this is the important part) rub the palms of your hands together to emulsify the product, like you're going to wash your hands with it, just for a few seconds, then apply to your wet head. With a shampoo apply to the scalp then use your fingertips to really work the product into the roots and scalp, with Dandrene you will want to concentrate on on any areas that are itchy too. Leave it on the scalp for 1-2 minutes. Hint, do it at the very beginning of your shower. You should do this at least 3-4 times per week. Condition the ends of your hair only, using the same application process as shampooing, rinse.
Other considerations: Drink lots of water, especially in the heat drink extra. Take a multivitamin just to eliminate the possibility of a deficiency. Look into your diet, oftentimes the food we ingest causes an allergic reaction which results in some curious conditions. If you're concerned about dietary triggers see a nutritionist, a food allergy specialist, an acupuncturist or a homeopathic physician, it's likely that none of them will require a referral to be seen so just call to make an appointment.