Interesting to hear!

This may be off, but I had itchiness after soaking in the tub &/or having really long showers.. When I just showered quickly it was okay...
(I used almost no soap or such, but didn't really bother to wash the tub well beforehand! & others in the household do use soaps & strong bad shampoos & such..)

Also had some itchiness yesterday, I think because I ate some chocolates.. (of unknown origin/unknown additives)
So maybe pay some attention to your shower/tub & eating...?
(at least it seems to be a factor in my case... maybe chlorine too.. - I heard more chlorine is present in water at night & more gets excreted in hot water.. Not sure if it's true but it was interesting to hear..)

When I was a kiddie I got real itchy rash after eating anything with artificial additives..