Potatoes contain two types of problem compounds for eczema-prone skin. The first is an allergenic protein called patatin that makes up about 40% of the potato's soluble protein and can trigger immune reactions. The second — and often more relevant — is glycoalkaloids (solanine and chaconine), natural toxins concentrated in the skin that can damage the gut lining and increase permeability, potentially allowing food particles into the bloodstream that drive immune reactions and eczema flares.

Peeling potatoes removes a significant portion of glycoalkaloids. Green-tinged or sprouted potatoes have much higher levels and should be avoided entirely. Sweet potatoes are an unrelated species with a completely different protein profile — they are a safe substitute and are generally well tolerated.