Apply Calamine lotion

In infancy it's generally more acute and on the face. As the child grows older it becomes milder and involves folds of extremities

Think about what could have triggered it and avoid the trigger. Like any change in soap, moisturizer, any supplement, bedsheets, detergent etc. unless the trigger is avoided, healing is difficult. Despite avoiding the trigger and using the lotion, if its not getting better, mild steroid cream needs to be applied after consultation. And yes, its a chronic condition only if you do not avoid the trigger and don't keep him moisturized. You can use physiogel moisturizer.