There does not appear to be any one underlying cause for delusional parasitosis, although it probably has to do with fundamental aspects of brain chemistry. This syndrome is often classified into three types according to the underlying condition:

Primary Ppsychotic Delusional Parasitosis
(Delusional parasitosis is the sole psychological disturbance)

• patients otherwise behave normally
• reason in a rational manor

Secondary Functional Delusional Parasitosis
where is an underlying psychiatric condition, including:

• schizophrenia
• paranoia
• depression
• anxiety disorders
• obsessional states

Secondary Organic Delusional Parasitosis
where there is an underlying physical illness is present, including:

• drug abuse
• hypothyroidism
• cancer
• cerebrovascular disease
• tuberculosis
• neurologic disorders
• vitamin B12 deficiency
• diabetes mellitus