It looks rather like exzema. I would use water only in the bath/shower or a ‘simole’ soap (shower gels leave residue) I would also try Ecover washing liquid abs the same on fabric conditioner. My dd2 gets the same thing and it’s inevitably linked to one of the two.
I’ve used Dermalex to avoid the hydrocortisone creams but if it’s really stubborn, they are the only ones that work. Very, very thin application and wash your hands after use. You may need hydrocortisone cream initially to bring down the inflammation and itch. Soaking in the bath with lots of bubbles won’t help at all so I would go for either a bath a day or 2 short showers (5 mins) as per preference. Alternatively, there’s always the GP if you think it may not be Eczema. X
Best thing I've found for ds excema as a general moisturiser is aveeno with the green lid. I've tried all kinds from the docs but this has really kept it under control. Different creams seem to work differently on everyone though.