People with schizophrenia may also have problems with memory, attention, and concentration, notes the American Psychological Association. (2)

What Causes Schizophrenia?

It’s not known exactly what causes schizophrenia. For some people, schizophrenia may have a genetic factor. Having a parent or sibling with schizophrenia may slightly increase a person’s risk of developing it. Researchers have found several genetic changes that may lead to an increased risk of the condition, according to the U.S. National Library of Medicine. (3) Symptoms of schizophrenia may be severe or even disabling — and schizophrenia can be tricky to diagnose. But many of the symptoms can be controlled over time with proper treatment. They usually first appear in a person’s late teens through early thirties. People with schizophrenia may display psychotic symptoms, which can be particularly troubling for friends and family. Doctors call these symptoms “positive” symptoms. Positive symptoms of schizophrenia include:

Hallucinations

This is when a person sees, hears, smells, or feels things that aren’t really there. Auditory hallucinations — hearing sounds that are not really there — are the most common type of hallucination in people with schizophrenia. One study notes that an estimated 60 to 80 percent of people with schizophrenia may experience auditory hallucinations. (4) Hearing voices is the most common type of auditory hallucination in schizophrenia. This could come in the form of hearing a clear voice or hearing many less clear voices, like the noise found on a busy subway. Other less common types of auditory hallucinations include music, body noises, or machinery. (4) People with schizophrenia also may feel sensations of pain or invisible fingers touching their bodies when no one is nearby, according to a study published in December 2016 in Scientific Reports. (5) Visual hallucinations, which are uncommon in schizophrenia and tend to be found more in neurologic illnesses, like certain forms of dementia, tend to be vivid and colorful, and may include scenes with family members, religious figures, or animals, past research has noted. (6)

Delusions

These are beliefs — sometimes bizarre — that are illogical or untrue. For example, a person with schizophrenia may believe he or she is being watched by another person or animal who’s not there, followed by the government for not paying taxes, or even controlled by aliens. The majority of people with schizophrenia experience delusions, per StatPearls. (7) People with schizophrenia may have paranoid delusions, believing that others are trying to harm, spy on, or plot against them. Paranoid delusions are important because they can make it difficult for a person with schizophrenia to cooperate with treatment. Poor adherence with treatment can increase the likelihood of social problems, such as joblessness or homelessness, for people with schizophrenia, according to the National Alliance on Mental Illness. (8) RELATED: Schizophrenia: Popular Myths, Real Facts

Disorganized Thinking and Speaking

People with schizophrenia may have trouble organizing their thoughts in a logical pattern. They may talk in a jumbled way that’s difficult to understand. One severe thought disorder is referred to as “word salad.” Disorganized thinking (which manifests as disorganized speech) exists on a spectrum, anywhere from tangentiality, to loosening of associations between sentences and words, to loss of any coherent meaning.

Unusual Body Movements

People with schizophrenia may make agitated or repetitive movements.

Memory, Attention, and Other Cognitive Problems

Cognitive symptoms are very common in schizophrenia. These symptoms include difficulties with memory, attention, executive function, and processing speed.

Other Symptoms

Other schizophrenia symptoms — sometimes referred to as “negative” symptoms — can include:

Speaking little, even when forced to interactLack of emotional expression when talking (face may not move, voice may be dull and monotonous)Lack of pleasure in everyday activitiesDifficulty focusing or paying attentionDifficulty using information to make decisionsNeglecting physical appearance or hygieneSevere lack of energy

People with schizophrenia may also enter a state in which they don’t move at all, don’t respond to others, and seem to be in a trance. This coma-like daze is called catatonia. (5) While catatonia typically involves limited spontaneous movement or speech, patients in this state often respond abnormally, for example, repeating words or movements back to the examiner. RELATED: Speaking Schizophrenia — A Glossary of Terms to Describe Symptoms, Tests, and Treatment Paranoid schizophrenia used to be classified as a subtype of schizophrenia. Today, health professionals no longer recognize paranoid schizophrenia as a separate subtype. The classification changed in 2013 when the American Psychiatric Association stopped recognizing schizophrenia subtypes. (5) Paranoid schizophrenia and other subtypes weren’t very helpful to doctors, because schizophrenia symptoms can change over time, and symptoms of different subtypes can overlap. RELATED: How Resilience Helped Me Transform My Life After a Brain Injury