A simple cheek swab could one day provide a quick and noninvasive diagnostic test for schizophrenia. A new study published in Science Advances has identified higher levels of two biological markers in the cheek swabs of patients with schizophrenia compared with people who don't have this mental health disorder. Schizophrenia is a long-term condition with a range of symptoms including hallucinations, delusions, muddled thoughts and loss of interest in everyday activities.