Indications for a brain‐hair follicle axis: inhibition of keratinocyte proliferation and up‐regulation of keratinocyte apoptosis in telogen hair follicles by stress and substance P

The document from 2001 demonstrates that stress can lead to hair loss by affecting hair follicles, as evidenced by experiments on mice. The study found that sonic stress caused an increase in apoptotic cells and a decrease in keratinocyte proliferation in hair follicles. Stress also led to immune changes, such as increased perifollicular macrophage clusters and mast cell degranulation, and a decrease in intraepithelial γδ T lymphocytes. These effects were similar to those caused by the neuropeptide substance P (SP) and could be reversed by a selective SP receptor antagonist. The study, which used mice in sample sizes ranging from 4 to 21, suggests a brain-hair follicle axis where stress inhibits hair growth through SP-dependent activation of immune cells. Additionally, stress increased the abortion rate in pregnant mice, indicating a systemic stress response. The findings highlight the potential of SP receptor antagonists as a treatment for stress-induced hair loss and related mood disorders.