Cow's milk is the most common food trigger for eczema in infants and young children. It contains proteins (casein and whey) that the immune system can mistakenly identify as harmful — and when this happens, the body launches an inflammatory response that shows up as red, itchy, inflamed skin.

Reactions can appear within minutes as hives or swelling, but many people experience a delayed flare where skin worsens 1–3 days after consuming milk — which makes it genuinely difficult to connect cause and effect without a food diary. About 2–3% of infants have a confirmed milk allergy, and roughly half of those also have eczema. Heating milk thoroughly (such as baking it into a muffin) destroys some of the problem proteins, which is why about 75% of milk-allergic children can eat baked goods containing milk even when they cannot tolerate a glass of it.