Summary: A Belgian study of trans men found that type of testosterone given does not affect hair growth, acne, or balding, and characterized further the skin changes that happen with testosterone therapy.

This was a study of the skin quality of trans men, performed in Belgium. Why study this topic at all? Because some of the effects of hormone therapy for trans men are skin-related. The skin may get oilier, acne may increase, hair grows in places it didn’t before and gets thicker and rougher, and for some men they start to have male-pattern baldness or a receding hair line. These effects have also been seen in cisgender women with polycystic ovarian syndrome, where they have high levels of testosterone. Turns out, though, that it’s not so much testosterone itself that causes these effects. It’s dihydrotestosterone (DHT), which is made from testosterone. You can think of DHT like a super-powered version of T. This is why medications like finasteride can sometimes prevent hair loss, by blocking the conversion of T to DHT.

The WPATH Standards of Care estimates the following timeline for various skin-related changes from starting testosterone as such:

Acne increases in the first 1-6 months, peaking around 1-2 years on T

Body hair growth starts in 3-6 months, peaking around 3-5 years

Hair loss is highly variable, but would be expected to start after at least a year T.

So what about this study? What exactly were they looking at? This study looked at a long-acting form of testosterone which hasn’t been used in previous studies of trans men skin. Classically, hormone therapy for trans men is a weekly or biweekly intramuscular injection of testosterone cypionate or testosterone ethanate. Which testosterone you receive depends on the country (cypionate’s more common in the US), seed/nut allergies, cost, and personal/physician preferences. This study looked instead at testosterone undecanoate, which is given every three months. This study then asks two questions:

Is there any difference in the effects of skin between testosterone undecanoate and the more common 1-2 week injections? What effects on skin can we see from long-term testosterone use?

To answer those questions the researchers did both a longitudinal and cross-sectional study. Remember, a longitudinal study is one where a a group of people is “followed” over a period of time. It provides a good picture of how things change over that time period, but can be expensive. A cross-sectional study examines people only once. It provides a lot less data but is cheaper.

For the longitudinal study they focused on testosterone undecanoate. They followed a group of 20 trans men over the course of their first year on testosterone (undecanoate), asking them back to do bloodwork and questionnaires every 3 months. For the cross-sectional study, they examined 50 trans men only once. These men were all post-hysterectomy/oophorectomy and had been on testosterone an average of 9.9 years (3.2 – 27.5 years range). 35 of them were on a mix of testosterone esters every 2-3 weeks, 7 were on testosterone undecanoate, and 8 were on topical cremes. Exclusion criteria were the usual, and quite reasonable: excluding those with endocrine problems, prolonged use of corticosteroids, and the like.

What did the researchers look at specifically?

Degree of hair growth on the lips, chin, chest, upper back, tailbone area, abdomen, arm, and inner thigh (“Ferriman and Gallwey” method)

Satisfaction with their hair growth patterns

Evaluation of acne, including the back/neck areas

Quantity of sebum production. Sebum is oil that skin produces.

Bloodwork, including: sex hormone-binding globulin, luteinizing hormone, follicle-stimulating hormone, estrogen, and testosterone

Results? Well let’s look at this one subject at a time…

Hair growth? For the longitudinal group, it appeared to increase most dramatically between 3-6 months. However hair growth appeared to continue to increase past that point. The type of testosterone did not appear to be associated with different levels of hair or satisfaction in hair amounts. There was a lot of variation in the fuzziness of the participants with some men not increasing their fuzziness at all.

Male pattern baldness? One person in the longitudinal group started balding in his first year. Among those on testosterone for more than a year, roughly a third has severe balding, a third had mild/minimal balding, and a third had no balding at all. There was not association between the type of testosterone and balding, though the older the man was the more likely it was he would bald.

Acne? For the longitudinal group, it was worst at 6 months but rapidly improved after that. At that 6 month mark, 82% of the men had facial acne. During the first year, roughly half of the men used various acne control products. For those in the cross-sectional group, roughly 1/3 did not have acne. 2/3rds had minor acne. 2/3rds of the group also had no acne scarring.

Sebum production? Was evaluated only in the cross-sectional group, and was not elevated. It also wasn’t associated with acne, or hormone therapy type/duration.

Bloodwork and hormone levels? No associations were found between any sex hormone levels and any of the skin factors measured (hair growth, baldness, acne, sebum)…. with one exception. In the cross-sectional group, estrogen levels were associated with hair growth. The authors are uncertain what that result might mean, and it may well be a fluke. Further research will have to find out.

But what does it all mean?! Well remember the original two things the researchers were investigating? Scroll up if you need to. Basically, it means that there doesn’t appear to be a difference in skin effects between the different types of testosterone therapy. And a trans man starting on testosterone can expect mild acne which peaks around the 6 month mark. Hair growth will accelerate the fastest during the 3-6 month period, but will continue afterward. But if he’s going to go bald, it likely won’t be in that first year.

Study limitations? The authors were pretty honest about the limitations of their measures. Some were subjective (e.g., the Ferriman and Gallwey method used for hair growth) and did not assess all areas that may change (e.g., buttocks and hair growth). They also point out the usual limitations inherit to the cross-sectional part of their study – it’s very hard to determine causes. I would also add the limitations in their sample size (relatively small), ethnicity/race (not reported, but nearly all participants were from Belgium). I also did not see them account for smoking tobacco in their study, though they did report the smoking rates (25-28%) of their groups. A number of potential variables were not reported on, such as hygiene or familial hairiness.

However I don’t see any glaring errors in this study, and it seems to have been respectfully done. Its language usage is certainly more respectful than many studies I’ve read about trans health.

This article was published in the Journal of Sexual Medicine. Its abstract is publicly available.

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