Hair can become ingrown on any part of the body, according to "Foundations and Adult Health Nursing," though ingrown hairs are most common in areas in which pressure is commonly applied throughout the day, such as the underarms or back of the thighs. When left untreated, ingrown hairs can become quickly infected, often causing pain, redness, swelling and irritation. Though this condition can be treated, it is best to prevent ingrown hairs on the back of your thighs.
Exfoliate the back of your thighs with a loofah and body wash daily in the shower. According to "Cosmetic Dermatology: Principles and Practice," this keeps the backs of the thighs clean and reduces the risk of ingrown hairs.
Shave the backs of your thighs regularly to avoid having hair that could potentially become ingrown. Use shaving cream and a new, sharp razor blade when shaving your thighs to ensure the closest shave.
Apply baby powder to the backs of your thighs each after exiting the shower. According to "Cosmetic Dermatology: Principles and Practice," this prevents ingrown hairs by providing a thin protective layer between the tips of the hair and the skin that is difficult for the hair to penetrate.