Itchy Scalp - Allergic to Dandruff Shampoo? Or Don't Use Often ENOUGH? How do you know if your scalp is just itchy cause you don t use dandruff shampoo often ENOUGH, or if you re allergic to some chemical in the dandruff shampoo so it just keeps irritating the scalp? I only use dandruff shampoo, and I only shampoo about 2x a week. No dandruff but itchy scalp, so I continue to use it and it doesn t help very much. Last night I used the clinical strength head & shoulders (active ingredient 1% selenium sulfide for seborrheic dermatitis ) & it said to rinse and repeat. Instead I rinsed & used the regular head & shoulders (active ingredient 1% pyrithione zinc for dandruff). Had to get out of the shower it was so painful & I had red burn marks on my scalp. Maybe some kind of chemical reaction between those two?!