Hair thinning is a progressive, mild to moderate loss of hair that can cause your head to appear sparser or with thinner patches of hair. But it doesn't always result in baldness, unlike widespread hair loss. There are two possible causes of thinning hair: genetics and lifestyle. One major factor contributing to thinning hair is lifestyle choices. These include using too many colours, sprays, and straighteners on your hair, as well as wearing it too tightly.