Quantifying changes to hair and skin from HRT

Hair is one of the most common areas of concern during transition: hair length, facial hair, and body hair are often important aspects of desired self-image for trans people, and these visible features are seen by others as strong signifiers for the purposes of gender classification (or “passing”). However, key publications on medical transition protocols and outcomes, such as the Endocrine Society’s clinical guidelines (Hembree et al., 2017), still describe the effects of cross-sex hormone therapy on hair and skin only in vague and general terms. Within these guidelines, trans men are stated to be likely to experience skin oiliness, acne, facial hair and body hair growth, and scalp hair loss (Table 12), while trans women are conversely likely to have softening of the skin, decreased oiliness, a decrease in the growth of terminal hair (thick, long, and dark hairs), and “variable” changes in scalp hair.

While these broad descriptions encompass the wide variation between individuals in the changes experienced from HRT, they’re lacking in specifics. How great is the extent of these changes? What might the results actually look like? These questions matter greatly to trans people who are looking to acquire certain physical features and be rid of unwanted ones.

As it turns out, a study from nearly 20 years ago sought to answer these very questions. Giltay & Gooren (2000) observed and quantified changes in body hair and skin oiliness among 21 trans women and 17 trans men before starting HRT and after 4, 8, and 12 months. The authors’ key findings include:

• After 12 months, trans women’s overall body and facial hair density had decreased significantly. Cheek hair decreased from an average of 32 to 18 hairs per square centimeter, while upper abdomen hair decreased from 8 to 4 hairs per square centimeter. Hair diameter declined significantly after 4 months, from 90 to 67 microns for cheek hairs and from 56 to 28 microns for upper abdomen hairs, and then remained at this level at 8 and 12 months. By 12 months, hair growth rate slowed from 0.31 to 0.22 mm/day for cheek hairs and from 0.3 to 0.15 mm/day for upper abdomen hairs.
• Trans women’s skin sebum production, measured at the forehead, nose, chin, and back, decreased significantly after 4 months. Additionally, all six trans women who had acne at baseline no longer had acne after 4 months.
• After 12 months, trans men’s overall body and facial hair density increased significantly. Testosterone induced the growth of cheek hair, which reached a density of 27 hairs per square centimeter by 12 months, and upper abdomen hair, which reached a density of 7 hairs per square centimeter. Upper abdomen hair reached an average diameter of 34 microns by 12 months, while cheek hair increased from 17 to 47 microns. And after 12 months, the growth rate of both cheek and upper abdomen hair reached an average of 0.22 mm/day. The authors also note that leg and forearm hair increased markedly in trans men after just 4 months.
• After 4 months of testosterone, 94% of the trans men in the study had facial acne. Skin sebum production at the forehead, nose, chin, and back also increased significantly.

The authors also provide figures illustrating the extent of hair growth and skin sebum changes over time in one trans woman:

And in one trans man:

While this study did not examine the effects of HRT on scalp hair, previous studies have noted that trans men can begin to experience androgenic alopecia (male-pattern baldness) after starting testosterone, that this is “clinically and therapeutically similar to the common male-pattern-AGA in cis-gender men”, and that this hair loss can be successfully treated with finasteride (Moreno-Arrones, Becerra, & Vano-Galvan, 2017). Additionally, one case report showed a trans woman with scalp hair loss achieving significant hair regrowth after six months of HRT (Stevenson, Wixon, & Safer, 2016). Although the extent of any one individual’s changes from HRT aren’t entirely predictable, studies such as these help to provide trans people with a more specific idea of what is typical, as well as what is possible. ■