For instance, the global authority of public health, The World Health Organization, regard issues about transgender health in their manual for diseases and health issues (the ICD-11) as being separate from one's gender identity. The WHO believes that being transgender on its own shouldn't be approached as a mental disorder.

Additionally, the authority on psychology in the United States, The American Psychological Association distinguishes between gender dysphoria and gender nonconformity, saying "Gender dysphoria is not the same as gender nonconformity, which refers to behaviors not matching the gender norms or stereotypes of the gender assigned at birth. Examples of gender nonconformity (also referred to as gender expansiveness or gender creativity) include girls behaving and dressing in ways more socially expected of boys or occasional cross-dressing in adult men. Gender nonconformity is not a mental disorder." The APA lists gender dysphoria as being separate from simply not matching your gender assigned at birth in its manual for mental disorders, the DSM-V

Why do they do this? Because after decades of study of the behaviors and brains of transgender people, they gained a deeper understanding of why people are transgender and the psychological and biological foundations of it. You can read a summary of their findings here.

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