Gender-affirming hormone therapy (GAHT) leads to changes in body composition, secondary sex characteristics and in the distribution and pattern of hair growth. Transgender individuals undergoing GAHT may experience altered hair growth patterns that may be affirming and desirable, or undesirable with a subsequent impact on their quality of life. Given increasing numbers of transgender individuals commencing GAHT worldwide and the clinical relevance of the impact of GAHT on hair growth, we systematically reviewed the existing literature on the impact of GAHT on hair changes and androgenic alopecia (AGA). The majority of studies used grading schemes or subjective measures of hair changes based on patient or investigator's examination. Very few studies used objective quantitative measures of hair parameters but demonstrated statistically significant changes in hair growth length, diameter and density. Feminizing GAHT with estradiol and/or antiandrogens in transgender women may reduce facial and body hair growth and also can improve AGA. Masculinizing GAHT with testosterone in transgender men may increase facial and body hair growth as well as induce or accelerate AGA. The impact of GAHT on hair growth may not align with a transgender person's hair growth goals and specific treatment for AGA and/or hirsutism may be sought. Further research on how GAHT affects hair growth is required.