What causes transsexualism?

On this page, I’m trying to give answers to the following question:

Is there a plausible biological mechanism that can cause a mismatch between mental gender identity and physical sex characteristics?

Spoiler alert: The answer is yes. I have tried to answer the question by making a list of observations and supporting them with evidence from current scientific research.

To clarify: The root cause for transsexualism has not yet been found. Similar to other conditions, such as homosexuality, autism, and diabetes, there seems to be a multitude of factors working together, which makes research more difficult. In case of transsexualism it seems that the major biological origins are genetics, epigenetics and pre-natal hormones. There might also be additional environmental triggers. The objective of this page is to show one or more possible, or even plausible, biological mechanisms that can cause gender dysphoria.


5. Hormone exposure before and around birth can influence the sexual differentiation of the brain, including gender identity
a. Human studies
– Reference list of scientific articles and studies (93 items)
b. Animal studies
– Reference list of scientific articles and studies (26 items)

6. Genetic factors can influence the sexual differentiation of the brain
a. Human studies
– Reference list of scientific articles and studies (11 items)
b. Animal studies
– Reference list of scientific articles and studies (16 items)


To provide evidence for the observations above, a number of scientific studies is listed. Please have a browse.

I very much appreciate corrections, amendments and additions.

All abstracts are taken verbatim from the respective studies, only the highlighting is mine. To avoid distorting the studies, the included abstracts are usually full-length, even if some parts are not relevant to the observation detailed in the chapter. Please read the original studies for more information; often the contents are even more interesting than the carefully worded abstract. Some studies are listed twice to illustrate separate points. I tried to provide mainly recently published and peer-reviewed studies and avoided case studies with few participants.

Articles are listed chronologically by chapter; key points relating to the observation made in the respective chapter are highlighted.

I would like to express my gratitude to all researchers and contributors to human biology and medicine – your work is continuously making this world a much better place for all of us. Thank you so much!

Navigation/Back to main pages

This page is part of the four main reference pages:

What is transsexualism? | What causes transsexualism? | What helps?

More evidence: Disorders of sex development (DSD)

A summary of the findings of the reference pages is given here: Summary

More references can be found here (articles not directly relevant to the observations discussed on the main reference pages): Other references

A short essay on the biological basis of transsexualism is here: Biological basis

A short discussion regarding possible contradicting evidence is here: Evidence against?

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