Why does warm weather aggravate eczema?

Sweat, mostly.: Irritation by sweat is the most likely mechanism. Sensitivity to seasonal fruits or vegetables, or warm-weather topicals (such as sunblocks) may also be responsible.

Sweating: Sweating is a common cause for aggravating eczema in the summer. In addition some sunscreens can make eczema worse as can sun exposure itself in some children. Finally chemicals that are in swimming pools also can irritate skin is sensitive children. For older children, pollen exposure during summer months may increase allergic symptoms including eczema.

Heat: Heat will often make eczema worse - it causes release of histamine from cells in the skin and histamine causes itching. Interestingly, humidity (which frequently comes along with warm weather) often makes eczema better. That said, every baby has his own triggers and sensitivities that exacerbate or improve eczema.