Common causes of hair breakage include excessive heat styling, frequent chemical treatments like bleaching or coloring, harsh brushing or combing, and overwashing with harsh shampoos. Environmental factors such as sun exposure, wind, and pollution can also weaken the hair. Additionally, using hair accessories and styles that pull on the strands too tightly, such as tight ponytails or hair extensions, can contribute to breakage. Poor diet and lack of hydration may also affect hair health, leading to breakage.