Several mechanisms for a psychological etiology of the condition have been proposed, including theories based on misdiagnoses of an underlying mental illness, stress, or classical conditioning. Many people with MCS also meet the criteria for major depressive disorder or anxiety disorder. Other proposed explanations include somatic symptom disorder, panic disorder, migraine, chronic fatigue syndrome, or fibromyalgia and brain fog. Through behavioral conditioning, it has been proposed that people with MCS may develop real, but unintentionally psychologically produced, symptoms, such as anticipatory nausea, when they encounter certain odors or other perceived triggers. It has also been proposed in one study that individuals may have a tendency to "catastrophically misinterpret benign physical symptoms" or simply have a disturbingly acute sense of smell. The personality trait absorption, in which individuals are predisposed to becoming deeply immersed in sensory experiences, may be stronger in individuals reporting symptoms of MCS. In the 1990s, behaviors exhibited by MCS sufferers were hypothesized by some to reflect broader sociological fears about industrial pollution and broader societal trends of technophobia and chemophobia.