He characterizes their way of thinking as being vague and void of thoughts and as sometimes having a "defective perceptual scanning". Because they often do not perceive cues that trigger affective responses, they experience fewer emotional reactions.For Millon, SzPD is distinguished from other personality disorders in that it is "the personality disorder that lacks a personality." He criticizes that this may be due to the current diagnostic criteria: They describe SzPD only by an absence of certain traits, which results in a "deficit syndrome" or "vacuum". Instead of delineating the presence of something, they mention solely what is lacking. Therefore, it is hard to describe and research such a concept.He identified four subtypes of SzPD. Any individual schizoid may exhibit none or one of the following:

Differential diagnosis
While SzPD shares several symptoms with other mental disorders, there are some important differentiating features:

Comorbidity
SzPD is often found to be comorbid with at least one of several disorders or pathologies. Sometimes, a person with SzPD may meet criteria for an additional personality disorder; when this happens, it is most often avoidant, schizotypal or paranoid PD. Alexithymia (the inability to identify and describe emotions) is often present in SzPD. Sharon Ekleberry suggests that some people with schizoid personality features may occasionally experience instances of brief reactive psychosis when under stress. Substance use disorder
Very little data exists for rates of substance use disorder among people with SzPD, but existing studies suggest they are less likely to have substance abuse problems than the general population.
A cold injury is defined as one in which cold temperature is the agent that causes tissue damage. Types of cold injury include chilblains, trenchfoot, frostbite, and immersion foot. Notes
References
Whayne, Tom French; DeBakey, Michael E. (1984). Cold Injury, Ground Type (PDF). Medical Department, United States Army, in World War II. Washington, D.C.: U.S. Army Center of Military History. OCLC 19967629. Retrieved 25 June 2021.