A hair prosthesis (or cranial prosthesis) is a custom-made wig specifically designed for patients who have lost their hair as a result of medical conditions or treatments, such as alopecia areata, alopecia totalis, trichotillomania, chemotherapy, or any other clinical disease or treatment resulting in hair loss. The terminology is used when applying for medical insurance or tax deduction status. Doctors have been prescribing these prostheses since the 1950s. Cranial prostheses also help to protect disease-weakened immune systems from the sun, and to regulate body temperature.