Many factors play a role in hair loss and hair thinning. Hair loss has a strong genetic component that can be inherited. Other factors contribute — including stress, diet, UV exposure, oxidative stress, toxins, pollution, hormones, aging, and various medical conditions. Hair follicles repeatedly go through stages in a cycle of growth and rest. It is the disruption of this cycle that results in excessive hair loss. The specialized cells in the follicle that become the hair shaft itself can be depleted during the resting or latent phase in the hair cycle, resulting in fewer and fewer active follicles (and hair) over time.