According to Hair Loss Prevention Centers, despite the urban myth to the contrary, shampooing one's hair does not cause or hasten baldness. In fact, avoiding shampooing and instead allowing hair to become dirty sometimes allows bacterial or fungal infections to grow on the scalp, which can cause hair follicles to die, thus hastening baldness. Other hair products such as gel and hairspray also do not cause or facilitate baldness.
The Telegraph explains that hair follicles exist in active and dormant states. Active hair follicles make hair regularly; although it is normal to lose 50 to 100 hairs a day, an active follicle replaces them. Dormant hair follicles do not produce new strands of hair but exist in a state of latency in which they are awaiting a chemical signal to start making hair again. As of 2012, researchers at L'Oreal were developing a shampoo designed to awaken a dormant hair follicle and make it active again.
While shampooing does not enable baldness, other hair treatments do. Treating the hair with heat, as when using curling irons and other mechanical appliances, can cause hair loss, according to U.S. News & World Report. Teasing also damages the hair and can cause it to fall out. However, despite another urban myth, wearing a hat does not strain the hair follicles, leading to baldness. Properly shampooing the hair and keeping it clean can reduce any infections promoted by wearing a hat.