Thanks for query.
There are several tasts for food allergy
. Recently at first allergic skin prick test is done to detect suspected allergen and subsequently it is confirmed by specific serum IgE assay. Though according to recent studies both these tests are equally effective. But there is no role of estimation of total serum IgE level.
Your baby's symptoms are suggestive of allergy because itchy skin, dermatitis
, eczema, headaches
probably due to recurrent sinusitis
are indicative of allergy. Therefore consult an allergist and take his opinion and go for those tests under his guidence.