I agree, sulfate free is the best way to go to keep your scalp feeling free of irritation. Try a clarifying shampoo that can remove buildup and restore the ph balance to your scalp.
Carol's Daughter Rosemary Mint
Bumble & Bumble Sunday Shampoo
Alterna Caviar Clinical Daily Detoxifying Shampoo
I get a really dry scalp with oil buildup during the winter since I never wash my hair more than 3x a week (more like 2). I found the Bumble & Bumble tonic lotion works well on the scalp to help it heal. It has teatree oil in it which can be drying if used too much, so I only use it twice a week. I was also concidering buying the Alterna root stimulator, but found one of the travel sizes of the B&B & really liked it.
I agree with bchen. Sulfates can do more harm than good on scalps and when you have a sensitive scalp, it can cause irritation. I use sulfate free shampoos and it is the best! My hair looks a lot healthier than what it has ever been before. Also, my scalp is content.
Look for sulfate free shampoos, sulfate can be really harsh on your skin, they use the same thing in household cleaning agents. I've also read about Lush's Shampoo Bars, haven't had the chance to try it yet, but seems to work with ppl with sensitive skin.