1. Etiology & the AFAB Adolescent Surge

What's known and hypothesized about why adolescent gender dysphoria looks fundamentally different from the historical clinical picture.

The historic clinical picture (pre-2010)

For most of the 20th century, gender dysphoria (formerly "gender identity disorder," "transsexualism") was a rare condition with a fairly stable clinical profile. The classical presentation: early-childhood onset (often by age 4–6), persistent across development, predominantly natal males, often associated with same-sex attraction in adulthood. In the 1960s–2000s, over 90% of adult transsexual patients were male.

Pediatric clinics confirmed a similar pattern in children: gender dysphoria in boys was more common than in girls by roughly 2:1 to 4:1, and follow-up studies consistently showed that the majority of gender-dysphoric children (often called "desisters") reidentified with their natal sex during adolescence and grew up to be gay or lesbian adults rather than transgender (Steensma, Singh/Zucker/Bradley follow-up cohorts).

The shift: 2010–present

Aitken et al. (2015) documented the altered sex ratio in clinic-referred adolescents: between 2006 and 2013 natal females became the majority for the first time. The shift has since accelerated and been confirmed in clinics in the Netherlands, Sweden, Finland, the UK, the US, Canada, and Australia (Kaltiala et al. systematic review of epidemiology, 2023).

Critically, this new cohort does not fit the historical clinical profile:

• Onset: typically adolescent (12–17), not childhood. Many parents report no prior gender-related distress before the announcement.
• Sex: predominantly natal female (roughly 65–75% across recent studies).
• Comorbidity: very high rates of anxiety, depression, eating disorders, self-harm, trauma history, and autism/autistic traits — far higher than the historical cohort.
• Social context: frequent peer-group clustering, online community immersion (Tumblr 2014–2017, then YouTube/TikTok 2018–present).
• Trajectory: rapid escalation from self-identification → social transition → request for medical transition, often within months.

The major etiological models

1. The biological / "innate gender identity" model

This is the model underlying the affirmative-care framework. It holds that gender identity is biologically established (probably prenatally, via sex-hormone exposure or genetic effects on neurodevelopment) and that misalignment with the body causes the distress. Supporting evidence includes neuroimaging studies showing that some trans adults' brain structure is shifted toward the identified gender on certain measures (Burke et al., 2022 and others). However: the effects are small, studies are limited and often confounded by sexual orientation or hormone exposure, and a 2025 review ("Brain Sex: Differences That Do Not Differentiate") argues the brain-sex literature does not robustly support a "trans brain" claim. Most importantly, this model does not explain why the AFAB adolescent cohort suddenly emerged — a true biological condition wouldn't shift demographically over a decade.

2. The developmental / psychological model

This is the older clinical model, dating to Stoller, Coates, Zucker, and others. It treats gender dysphoria as one possible manifestation of a more general identity-development difficulty, often arising from attachment disruption, sexual trauma, body shame, family dynamics, or unresolved sexuality questions. Within this frame, dysphoria is understood as a symptom to be explored, not a fixed identity to be affirmed. Many adolescent-medicine clinicians (e.g., the writers in the Marchiano/O'Malley/Ayad volume) work from this frame.

3. The social/cultural model

This model holds that the recent surge — particularly in adolescent girls — is best explained by changes in cultural context: the rapid rise of trans-identity content on social media, peer-group identification dynamics, the appeal of marginalized-identity status to teenagers searching for meaning, and the simultaneous decline in psychological frameworks that gave teens other ways to make sense of body distress, social difficulty, or same-sex attraction. Leor Sapir's review and Jonathan Haidt's The Anxious Generation argue this is the most plausible explanation for the demographic data.

4. The "many roads in" model (now the leading clinical view in cautious systems)

This is the model adopted implicitly by the Cass Review and most European clinics that have revised their guidelines. It holds that "gender dysphoria" in adolescents is heterogeneous — what looks like one diagnosis actually captures several distinct populations with different drivers and different optimal treatment paths. These may include:

• A small minority with classical, persistent early-childhood gender dysphoria.
• A larger group with autism-spectrum-related identity confusion (see Section 2).
• A group whose dysphoria is downstream of trauma, abuse, or attachment difficulty.
• A group whose dysphoria is downstream of unresolved same-sex attraction and internalized homophobia.
• A group whose identification is primarily socially mediated through peers and online community.
• A group with comorbid eating disorders, body dysmorphia, or other body-focused conditions.

These groups overlap substantially. The clinical implication: treatment cannot be one-size-fits-all, and the assessment has to be unhurried, holistic, and willing to explore alternatives. This is the framework underlying the Cass Review's recommendations for the UK NHS.

What the systematic reviews concluded

Between 2019 and 2025, every major government-commissioned systematic review of the evidence base reached strikingly consistent conclusions:

• UK / Cass Review (2024). "Remarkably weak evidence" for medical interventions in adolescents. Puberty blockers do not "buy time," compromise bone density, and the vast majority of youth proceed to cross-sex hormones. No evidence that transition reduces suicide. Recommended a holistic, mental-health-led model. Puberty blockers restricted to research-only settings in the NHS.
• Sweden / SBU (2019), Karolinska (2021), National Board of Health (2022). Sweden's Karolinska Hospital ended puberty blockers and cross-sex hormones for minors outside research trials in 2021. National policy followed in 2022.
• Finland / COHERE (2020). The first country to revise guidelines, prioritizing psychotherapy for post-pubertal-onset cases.
• US / HHS (2025). A 400-page review concluded the quality of evidence on benefits is low and evidence on harms is sparse. Subsequently disputed by major US medical bodies (AAP, APA), but the underlying methodology — applying GRADE evidence standards — mirrors what the European reviews did.

The Tavistock collapse — a cautionary case study

The UK's Tavistock Gender Identity Development Service (GIDS) was the world's largest pediatric gender clinic. An independent review found that GIDS was "not a safe or viable long-term option" and recommended closure (executed by Spring 2024). Critical findings:

• Predominantly affirmative, non-exploratory approach driven by patient and parent expectations.
• Limited evidence of routine mental-health or neurodevelopmental assessment.
• ~2,000 children referred for puberty blockers without robust supporting data.
• No systematic outcome data collection — even when evidence emerged of poor outcomes, the service did not change practice.
• Multiple clinicians (Hutchinson, Bell, Marcus Evans, and others) resigned in protest and have since written extensively about the institutional dynamics that produced these failures.

So what is causing it?

Honest answer: no one knows for certain, and the cause likely differs from individual to individual. What the evidence does support:

1. The historic clinical model (innate, early-childhood, predominantly male, persistent) describes a real but small population — and does not describe the modern AFAB adolescent cohort.
2. The modern cohort has very high rates of comorbid mental-health conditions, autism/autistic traits, and prior childhood-development issues — these almost certainly play a causal or contributing role, not just an associated one.
3. Social and cultural factors (peer groups, online content, the broader cultural foregrounding of gender identity) are very likely contributors to the timing and form of the surge, though the precise mechanism is debated.
4. Treating adolescent-onset gender dysphoria as definitionally the same condition as classical, childhood-onset gender dysphoria — and applying the same treatment protocol — is increasingly viewed as a clinical error by the European systematic reviewers.