In the next set of experiments we focused on pruriception because of the prominent functions of GCH1 and BH4 in the skin.2, 53 Our results reveal that GCH1‐derived myeloid BH4 is a regulator of pruritogen‐evoked itching responses, raising the intriguing question of its specific functions in the context of allergy or skin diseases. This evidence concerns the gene GCH1 and allergic disease.