Oats contain a protein called avenin that is similar to wheat gluten, and about a third of wheat-allergic people also react to oats. But oats carry a unique additional risk that is especially important in eczema: many skincare products contain colloidal oatmeal (brands like Aveeno). When oat proteins are applied to broken, inflamed eczema skin, they can sensitise the immune system — essentially training it to attack oat proteins. Research found that 32% of children who used oat-based skin creams showed positive skin patch tests to oats, suggesting immune sensitisation through the skin rather than through eating.

This means someone using oat-based moisturisers could later develop a food reaction to eating oats. Certified gluten-free oats are lower risk for wheat cross-contamination but do not reduce the oat protein itself.