Question

there is evidence that the risk of schizophrenia is increased by

Answer 1

There are multiple established risk factors (genetic and environmental). Major ones with good evidence include:

- Family history/genetics — strongest risk factor. Having a first‑degree relative with schizophrenia raises lifetime risk substantially (general population ~1% → roughly 6–10% for a first‑degree relative; monozygotic twin concordance ~40–50%).
- Adolescent cannabis use — consistent, dose‑dependent association (especially heavy/early use); roughly a doubling of risk for later psychosis in many studies.
- Obstetric and perinatal complications — e.g., prenatal hypoxia, neonatal respiratory distress, low birth weight; modestly increased risk.
- Prenatal infections and maternal immune activation — maternal influenza, rubella, toxoplasma and other infections during pregnancy are linked to higher risk.
- Advanced paternal age — risk rises with paternal age (especially >40–50 years), with modestly increased odds.
- Urban birth/upbringing and social adversity — being born/raised in an urban environment and long‑term social deprivation are associated with higher risk (dose‑related with degree of urbanicity).
- Migration and minority status — some migrant/minority groups have 2–3× higher risk, likely from social stress and exclusion as well as other factors.
- Childhood trauma and severe stress — physical/sexual abuse, bullying and severe adversity in childhood are associated with higher risk.

These factors interact with genetic vulnerability; none is determinative on its own. If you want, I can give effect sizes/references for any specific factor.