We all experience an itching sensation and the urge to scratch. An initial stimulus ignites our sensory neurons causing what may be called the scratch reflex.
The scratching can often lead to relief or be pleasurable due to a release of dopamine into the system. It can however also lead to continuous scratching and the feeling of more itches in the same and other parts of the body. Itching can also be “contagious” and often seeing someone else scratching can subconsciously lead to an itching sensation in a similar body part of anther person. An example of this could be when someone has lice and another individual close to the person infected with lice also begins to scratch. A theory on this may be that observing someone scratching causes neurons to fire in the same body part of the viewing individual that induces the same sensation. But theories on this are not confirmed.
Itching has multiple causes with including lice, allergies, dry skin, illnesses, and/or insect bites. While often itching sensations and scratching are temporary, scratching can become excessive and chronic and begin to damage the skin and expose the individual to more germs and infection. Itching therefore often has an underlying physical cause, however at times no physical cause can be found for the itching sensation and the act of scratching.
When no physical causes can be found after having gone to see a medical professional such as a general practitioner or a dermatologist among others, it is possible that the itching sensation may be due to physiological causes. This is referred to as a psychogenic itch, which is an excessive impulse to scratch, gouge or pick at normal skin due to possible psychological abnormalities.
Psychogenic itch does not appear to be a commonly studied topic on its own and therefore there are many unanswered questions. The prevalence of psychogenic itch is also unknown particularly in South Africa, however a study by Yosipovich and Samuel (2008) described that approximately 2% of patients seen at dermatology clinics in the USA were diagnosed with psychogenic itch with most of the individuals being diagnosed with psychogenic itch being women between the ages of 30 and 45.
Psychological factors may be associated with onset, severity and maintenance of itching. The itching when chronic and severe may cause impairments in the individuals social and occupational functioning; and it may cause marked lesions, scars, or rashes on the individuals skin. Emotional triggers can initiate itching, usually during life-stages of excitement, anxiety, stress and sadness or depression. Often, the areas of psychogenic itch are areas reachable to the patient, such as head, face, scalp, arms, legs, upper back, etc.
Psychogenic itch appears to be in provoked in reaction to chemicals such as serotonin and norepinephrine which induce states such as stress, depression, and a psychotic state known as delusional parasitosis, which is a false belief of parasite infection.
Psychogenic itch on its own is not necessarily common (in my practice as well) however it is associated with many different psychological disorders and is seen within these disorders. It is often associated with impulse control behaviours and obsessive traits. The most common of these disorders appear to be Depression, Obsessive Compulsive Spectrum Disorders (Obsessive-Compulsive Disorder, Hair-Pulling Disorder (Trichotillomania), Skin-Picking (Excoriation) Disorder), Body Dysmorphic Disorder, Stimulants (Substance use, Attention Deficit Hyperactivity Disorder), and Psychotic Disorders.
The treatment for psychogenic itch would first require ruling out any other (physical) causes of the itching sensation. Then seeing a psychiatrist for possible medication, such as anti-depressants (SSRIs) (but I cant comment on this as I am not a psychiatrist) and a psychologist for psychotherapy. The psychotherapy will often depend on the cause and the comorbidity of the problem (e.g. OCD, BDD, Trichotillomania, etc. Cognitive and Behavioural Therapy (CBT) with relaxation techniques have been found to be effective with treating conditions of depression, impulse and obsessions/compulsions and may be particularly helpful for individuals suffering from a psychogenic itch.
Yosipovich, G and Samuel, L. S. (2008). Neuropathic and Psychogenic Itch. Dermatologic Therapy, 21, 32-41.