The role of IgG in allergy has been controversial due to their binding affinity to different Fcγ receptors (FcγRs) which may lead to different immune response outcomes, depending on whether the FcγRs are activating (FcγRI and FcγRIIIa) [53] or inhibitory (FcγRIIb) receptors [54,55] on the immune cells [53,56,57]. This evidence concerns the gene FCGR2B and Allergy.