Educate yourself about a common form of eczema many of us develop later in life. Allergic Contact Dermatitis, ACD. You will never guess what is triggering your scalp itch. Simply treating the itch won't stop the cause. Like you I've had cancer and often with cancers our immune systems don't protect us like they used to. Also repeated contact with know elements both natural and chemical cause our body to raise up our histamine army trying to protect us and eliminate them from our system and thus we get rashes or burning or itching or pain.
Google the 5 Day Extended Patch Test, one such common test kit is the True Test Kit. It's an expensive test, around $1,500 covered by most insurance plan as well as Medicare. With this test I learned that every shampoo I was using, from Johnson's and Johnson's Baby Shampoo to Head and Shoulder's and others included allergic contacts. You could be allergic to the coconut, fragrance or as in my case several preservatives triggered my allergies. With testing you will be registered and given a code in which to go to a site and products that are safe for you are suggested.
Do not settle for a diagnosis of dermatitis!!! I did for years because my dermatologists, and I saw several over 10 years never told me about this test which only specially licensed allergists or dermatologists can administer. Out of about 80 plus patch sites I now know about 15 natural and chemical elements I must avoid for life. No more scalp itch for me. I used to pull on my hair while watching TV at night with my husband as it helped to distract from the itch, He would warn me I would go bald but the itching was maddening.
In the meantime you need to eliminate allergic sources and just shampoo with a basic old fashioned soap like Grandma's Lye soap, this bar soap only contains lard and lye and the lye becomes glycerin during the traditional soap building process, Google this Mayo Skin Safe product for an explanation. Also VMV Clark Wash is about the safest shampoo I am aware of on the market sold on the internet. Tea tree oil has been recommended, but Google the fact that some are allergic/eczema. I can also safely use their conditoner, but you may not! We all have a unique combinations of allergens causing our allergic dermatitis Read and study every ingredient and every product you use on your hair. Go to internet and check for allergic reactions. Self education, along with testing is the key to overcoming it like I have.
If you were told you had cancer your first question would be, "What kind?". Don't settle for simply being told you have dermatitis of which there are dozens of types. Yes, you probably do have a form of dermatitis, but you need a specific name of your type of dermatitis. Dermatitis and eczema are interchangeable words.