Most patients with eczema will know that they should stay away from soaps. Hopefully I can explain why this is. Essentially this is because oil and water do not mix. When dirt and oils accumulate on skin, water cannot easily wash them off.
This is why soaps contain surfactants. Surfactants allow the water to bind with the oil and dirt and wash them away. This is great for dirty skin but not great for patients with eczema. Eczema patients lack an adequate skin barrier. They have less natural moisturizing factors and lack certain proteins in their skin. With this impaired skin barrier, soap washes away too much of the little natural oils that exist in the skin, leaving eczema patients with a dry itchy skin.
This then allows the preservatives and fragrances in the soap to make the eczema even worse. So the solution? A soap free bath. I commonly would advise aqueous cream or cetomacrogol ointment as a soap substitute. Try it and notice the difference.