Paranoid schizophrenia, or schizophrenia with paranoia as doctors now call it, is the most common example of this mental illness.
Schizophrenia is a kind of psychosis, which means your mind doesn't agree with reality. It affects how you think and behave. This can show up in different ways and at different times, even in the same person. The illness usually starts in late adolescence or young adulthood.
People with paranoid delusions are unreasonably suspicious of others. This can make it hard for them to hold a job, run errands, have friendships, and even go to the doctor.
Although it's a lifelong illness, you can take medicines and find help to stop symptoms or make them easier to live with.