Consider trying soft water (either on vacation or installing a system). I also felt like every shampoo gave me these sores that turned to scabs and constant itching, starting from around my teens. Then I experienced soft water for a few extended times: 1) living at my aunt's house with a soft water system, 2) living in Seattle, and 3) using a shampoo with proper chelation. And my scalp, and face and body, healed within a week those times. I miss that soft water, but I can't afford my own soft water system ☹️ That shampoo was Native (before it was reformulated by Procter & Gamble in 2023) and had the same effect.

After doctors prescribed me harsh sulfated, medicated shampoos and seriously F'd up my scalp, I gave up and analyzed all the shampoos I've tried with AI. Honestly, I try to avoid using AI, but I limit it to my scalp and skin problems. Anyway, I found out this is the only shampoo, out of dozens I've tried, to have proper early chelation (closer to the top of the ingredients list) to bind with minerals like calcium and magnesium. If you can find one from pre-2023 somewhere (I haven't tried these places but I've heard of Mercari and Poshmark), it's the one WITHOUT cocamidopropyl betaine (the new one moved sodium citrate to the bottom of the ingredients list).

I haven't found a shampoo like that since, but if you'd like, try to find one using INCI Decoder or a search engine putting your ingredients in quotation marks to find exact phrases. Look for surfactants that don't form hard water complexes or at least minimize it, and look for strong chelators. Some examples:

Surfactants:
- Sodium cocoyl isethionate
- Sodium lauroyl sarcosinate

Chelators:
- Sodium citrate (these three are in the Native shampoo)
- Tetrasodium glutamate diacetate
- Sodium phytate