We noted that only tissues with HFs expressing high levels of NK1R, an SP receptor, are characterized with slow proliferation and active complete hallucinogenic keratinization, which has been attributed to terminal differentiation; additionally, several studies have reported that SP and CRH, initiators of AA, not only disrupt the IP of HFs, but also promote the apoptosis of the HF cells. This evidence concerns the gene TFF2 and hydrops fetalis.