Context. Hormone treatment induces feminization of the body in transwomen (male assigned sex, female gender identity) and masculinization of the body in transmen (female assigned sex, male gender identity). Unfortunately, the effect of hormone treatment on facial characteristics in transwomen and transmen is still unknown.

Objective. The aim was to objectify whether hormone treatment induces facial feminization in transwomen and masculinization in transmen, and how this potential change affects satisfaction and self-esteem.

Methods.  We performed a single-center cohort study in which we studied 27 transwomen and 15 transmen who started hormone treatment according to usual standard care in the Amsterdam UMC, Vrije Universiteit. 3D facial images were obtained at baseline, 3 months and 12 months. The main outcome was relative local shift of skin in millimeters.

Results. After 12 months, cheek tissue in transwomen increased with 0.50mm [95%confidence interval (CI) 0.04 to 0.96] in the x-axis and 1.08mm [95%CI:0.31 to 1.85] in the z-axis. Tissue in the jaws decreased with -0.60mm [95%CI:-1.28 to 0.08] in the x-axis and -0.18mm [95%CI -0.03 to 0.33] in the y-axis. Cheek tissue in transmen decreased with -0.45mm [95%CI:-1.00 to 0.11] in the x-axis and -0.84mm [95%CI:-1.92 to 0.25] in the z-axis. These changes already started after three months. An increase in satisfaction with the face was found in both transwomen and transmen. There were no changes in reported self-esteem.

Conclusions. Hormone treatment in transwomen induces an increase in cheek tissue and a decrease in jaw tissue. In transmen a tendency of decrease in cheek tissue and an increase jaw tissue was found.  These changes suggest that hormone treatment induces facial feminization in transwomen and masculinization in transmen. Furthermore, this research shows that 3D imaging is a promising tool for the evaluation of facial changes.