Schizoid personality disorder

Schizoid personality disorder is a Cluster A personality disorder which is not being interested in social relationships, often being alone. They are also secretive and don't show many emotions. It is often shortened to SzPD or SPD. 
This condition is not schizophrenia. People with SzPD will typically share some of the symptoms of schizophrenia. However, schizoids do not have the positive symptoms of schizophrenia such as hallucinations. A negative symptom is one that is taken away from a person. A positive symptom is one that is added to a person. 
People who have SzPD do not want interpersonal relationships which require emotion and commitment. People with SzPD are introverts who feel the need to be independent or alone. Many schizoids are asexual or have little interest in sexual encounters. Any relationships they may have probably does not involve emotional attachment. SzPD is more common in men than women. Some of the negative symptoms of the disorder (such as low energy) may be treated with some antipsychotic drugs.
Theodore Millon said that there are four types of schizoid: languid, remote, depersonalized, and affectless.
Salman Ahktar said that there were two types of schizoid: overt, and covert. Overt means visible, covert means secret or invisible. Covert or secret schizoids are active in social conversation and the outside world. However they do not tend to get emotionally attached to people. Acting differently in public is known as masking. 
Diagnosis.
The Diagnostic and Statistical Manual of Mental Disorders is a manual for diagnosing mental disorders. DSM-5 still includes schizoid personality disorder with the same requirements as in DSM-4. To be diagnosed with SzPD, one must have these behaviors consistently and be troubled by them. They also need to have at least four of these symptoms.
Another way a person with SzPD can be diagnosed is through the ICD-10 which is the International Classification of Diseases. The person must have the behaviors consistently. They must be troubled by them. They also need to have at least four of these symptoms.
Sometimes SzPD can be confused with other disorders such as Depression or Avoidant Personality Disorder. Sometimes people can have SzPD and other similar disorders. This is called being comorbid.
Treatment.
To manage their disorder, people with SzPD can take medication. One is called Buproprion. They can also go to psychotherapy. This means they talk to a therapist. The therapist helps them try to connect more with other people.