Nerves and muscles that raise goosebumps also stimulate stem cells in the skin to make hair follicles and grow hair.

Ya-Chieh Hsu, a stem cell researcher at Harvard University said getting goosebumps when it’s cold may encourage animals’ fur to grow thicker.

Hsu said nerves that are part of the sympathetic nervous system that control pupil dilation, heart rate and other automatic processes nestle next to stem cells that will create hair follicles.

The researchers found that the nerves secrete hormone norepinephrine, which is necessary for hair growth.