What gland causes goose bumps?

Goosebumps are caused by the contraction of tiny muscles at the base of hair follicles, known as arrector pili muscles. This reaction is typically triggered by the autonomic nervous system in response to cold temperatures or emotional stimuli, rather than a specific gland. While sweat glands can play a role in the body's response to temperature, it is the muscles, not glands, that create the appearance of goosebumps.