This page is a compressed portal into the research folder under research/hrt-timing-body-changes/. The deep pass removed several popular but weak claims: no more “clavicle fuses at 25,” no “sternum finishes at 25,” no hard age-coded Tanner ceiling, and no unsupported universal percentage for testicular shrinkage. What remains are the claims the current primary literature can actually carry.
The full age-banded narrative lives in age-windows-matrix.md. This table is the quick reference. Read the cells as “what a delay usually costs at this age,” not as a claim that every person in the band is at the same Tanner stage.
| Age band | Still meaningfully open | Closing | Mostly closed / later surgery-dominant | Main delay cost | Key anchors |
|---|---|---|---|---|---|
| 12-14 | Voice prevention, beard/body-hair prevention, major skeletal optionality, pubertal muscle trajectory | None uniformly closed | Usually few | High for voice, face, shoulders, hair | Puberty biology; voice change studies; blocker/BMD cohorts |
| 14-17 | Remaining skeletal optionality, hair prevention, body composition | Voice, long-bone growth, facial dimorphism | Some voices already changed | High for voice, beard, muscle accrual | Harries; Sorensen; Klink/Vlot |
| 17-20 | Body composition, skin, hair preservation, fertility planning | Late clavicle tail, some late thoracic maturation | Voice, height, most hand/foot growth | Moderate-high for hair, muscle, fertility | PMID 26188638; PMID 38960911 |
| 20-23 | Fat redistribution, lean-mass loss, skin, breasts, gonadal suppression | Late clavicle tail only | Voice and major bone structure | Mostly cumulative hair/body-comp cost | PMID 27572683; PMID 34415999 |
| 23-26 | Adult endocrine response remains strong | Scalp preservation advantage narrows | Bone and voice | Hair, skin, fertility | Adult trans cohorts |
| 26-30 | Fat, muscle, skin, breast growth | Mainly cumulative windows | Structural face / voice / shoulder goals | AGA, body-hair workload, skin history | Klaver; de Blok |
| 30-35 | Body composition and skin still very live | Scalp preservation, fertility logistics | Bone and voice | AGA and cumulative exposure | O'Connell review; fertility series |
| 35-40 | Endocrine effects, fat, skin, some breast growth | Hair preservation, modest breast ceiling | Structural goals | Hair, skin, bone-risk exposure | Brincat; Wiik; bone follow-up data |
| 40+ | Body composition, skin, bone maintenance, sexual-function effects | Fertility and scalp recovery | Voice and bone architecture | Cumulative hair/fertility/bone-health cost | Late-adult endocrine and bone-risk framing |
The decisive fusion signal is estradiol in both sexes. Morishima’s aromatase-deficient man and Smith’s estrogen-resistance case are still the classic human demonstrations that estrogen signaling, not testosterone by itself, closes plates (PMID 8530621; PMID 8090165).
Medial clavicle is one of the last routinely assessed epiphyses. In Ekizoglu’s thin-slice CT series, substage 3c first appeared at age 19 in both sexes (PMID 26188638). In Freiburg’s male CT cohort, only complete symmetrical stage 4 on both sides was a reliable marker of age >21 (PMID 38960911).
That supports a real late-teen / early-20s skeletal tail. It does not support “clavicle fuses at 25,” and it does not mean adult estradiol can noticeably narrow the bony shoulders.
Most hand, wrist, and long-bone growth is adolescent. Adult estradiol does not reopen fused plates, change adult height, or materially shrink hands and feet. Bone-density maintenance is a separate question from bone shape.
The sternum / ribcage claim was tightened on purpose: developmental sternebral fusion, manubriosternal fusion, and lifelong costal-cartilage mineralization are different processes. “Sternum ~25” was not defensible.
This is the strongest early cliff in the folder. Testosterone puberty changes the instrument itself: laryngeal framework, vocal-fold length, tissue mass, and tract resonance.
Sorensen and Horii measured children aged 7-15 and found median F0 values of 244 Hz in girls and 250 Hz in boys before major divergence (PMID 7558642). Adult reference studies center speech around about 190-225 Hz in women and about 105-135 Hz in men (PMID 7300286; PMID 3049278).
The Endocrine Society guideline remains explicit: feminizing hormones do not raise pitch after testosterone puberty (PMID 28945902). The reason is structural. Later estradiol may affect hydration and comfort, but it does not shrink the laryngeal framework back down.
Therapy and surgery still work. A recent meta-analysis found benefit for both, and a modern Wendler series reported about +33 Hz speaking F0 and +50 Hz sustained-vowel F0 at 1 year (PMID 39963873; PMID 35634734).
Skin is hormone responsive in adulthood, but not on a blank canvas. Sebum changes fast; collagen and dermal thickness change more slowly; photodamage is partly independent of current hormone state.
Pochi’s classic work supports puberty-related androgen increases in skin-surface lipids and sebum biology (PMID 143498). In trans women, Giltay and Gooren found objective sebum reduction within the first treatment year.
Brincat’s postmenopausal studies remain the best human analogue for estrogen effects on dermis. Treated women had mean skin collagen content about 48% higher than untreated controls in the 1983 study, and later work showed prevention or partial restoration of menopausal collagen loss (PMID 6416400; PMID 3828252).
That supports partial recovery. It does not support the idea that late estradiol erases decades of UV damage or acne scarring.
Hair timing runs in two directions: scalp follicles miniaturize under androgen exposure, while beard and many body fields terminalize. The same hormones do opposite things in different follicles because the follicles are biologically different.
AGA is cumulative, not a one-time puberty event. Earlier suppression preserves more follicles; later treatment more often stabilizes than fully regrows. That is why a delay at age 28 still matters even if it no longer matters for bone.
The strongest later-adult recruitment signal is not “every field keeps thickening equally forever.” It is that ear, nose, back, shoulder, and trunk fields often keep recruiting later than beard puberty. The 2023 GAHT hair review supports cautious wording: feminizing therapy may reduce body and facial hair and may improve AGA, but evidence is heterogeneous (PMID 37311161).
This is the strongest adult “not too late” system in the folder. Adult GAHT changes fat, lean mass, and visceral-to-subcutaneous patterning far more than many people assume.
Klaver’s meta-analysis found average 12-month changes of about +3.0 kg body fat and -2.4 kg lean body mass in trans women (PMID 27572683). In a large prospective cohort, trans women gained 4.0 kg total body fat while mean visceral fat stayed near flat, lowering the VAT/TBF ratio by 17% (PMID 34415999).
Wiik et al. found significant loss of muscle size and strength over 12 months, even though many measures remained above cis-female references after one year (PMID 31794605). For bone, the main pediatric caution is blockers without sufficient follow-on sex steroids: Dutch follow-up shows BMD Z-scores fall during GnRHa and recover after later GAHT, with transfeminine lumbar spine as the main residual concern (PMID 25427144; PMID 27845262).
The face is mixed. HRT can still move the soft-tissue layer enough to matter a lot. It does not reliably move the bony layer enough to replace structural surgery where bone is the issue.
Skin oiliness, facial-fat compartments, cheek softness, and masseter heaviness can all shift. That is why many adults see meaningful facial feminization over the first 6-24 months even though the skeleton is unchanged.
Brow bossing, deep nasion, gonial width, chin breadth, and thyroid-cartilage prominence are mostly bone or cartilage. Ousterhout and Capitán remain the classic references for why forehead surgery exists: these are structural targets, not skin targets.
This system is partially reversible but not all-or-none. Hormones commonly suppress fertility and gonadal activity. They do not guarantee immediate permanent sterility, and they do not guarantee later recovery either.
In Jiang’s orchiectomy series after more than a year of hormones, germ cells were still present in 81% of testes and spermatids in 40% (PMID 31310772). That is severe suppression, not universal complete absence.
Recovery after stopping GAHT is possible in some patients, but timelines are heterogeneous and one recovery series included a patient who required testicular sperm extraction after 17 months. Banking first remains the honest recommendation.
de Blok’s 3-year cohort showed continued breast-volume increase beyond year 1. Average gain was about 72 mL per breast, reaching roughly 100-101 mL by year 3, while breast-chest difference plateaued earlier (PMID 33206172).
Early suppression can reduce tissue available for classic penile inversion, but peritoneal-flap series show that genital hypoplasia does not remove vaginoplasty from the option set (PMID 36729740).
The plotting manifest now lives in graphs-and-data.md. The most useful curves are not decorative; they correspond to the real tissue classes in the folder.
244-250 Hz, then the sharp male pubertal drop toward ~120 Hz.3c first at 19; reliable symmetrical stage 4 as a >21 marker in thin-slice male CT.+3.0 to +4.0 kg fat mass, -2.4 kg lean mass, -17% VAT/TBF ratio over the first year.Voice and hard skeleton are the steepest early cliffs. Body composition, skin, and breast tissue remain more salvageable later. Hair is the clearest cumulative-exposure system: there is no single closure date, but years still matter.