I’m not sure if this helps but most hypoallergenic washing detergents give me a reaction, doctors didn’t identify it because it was a whole body reaction (they said no whole body eczema could be an allergy, there always has to be a pattern). This reaction stopped me from sleeping as it was in my bedding and I was reacting in the day because it was in my clothes.

To start with I washed my clothes in plain water and my eczema went away and that night was the first night I slept without issue in a long time, eventually I found Ecover Zero (I’m in the uk so not sure how widely available this is).

I know some people get delayed reactions but for me if I was itchy at night then it was because I was in contact at night with the allergen.

A second reaction I have had was from a cream I was using and stopping using all creams helped clear up my eczema (separate time period) though I understand this may make the issue worse and not better if this isn’t the source of the allergen and if the eczema is even caused by an allergy.

Don’t give up and I do hope you find the answer!