What Makes Us Itch?
Itching can be caused by many different things including allergies, insect bites, dry skin or illness.
While most itches are merely bothersome or uncomfortable, excessive scratching can damage your skin’s protective barrier and expose your body to germs and infection.
Itch and pain are closely linked in the brain. The reflex to pain is to withdraw. The reflex to itch is to scratch. This reflex is a protective response developed to help animals remove parasites from their skin. That’s why even a slight movement of hairs is enough to make you want to scratch.
Itching is often triggered by histamine, a chemical in the body associated with immune responses. It causes the itch and redness you see with insect bites, rashes and skin dryness or damage.
Histamine is released by the body during allergic reactions, such as those to pollen, food, latex and medications.
Types of Itch
Pruriceptive itch is due to an allergic reaction, inflammation, dryness or other skin damage. It is seen in atopic dermatitis (eczema), urticaria (hives), psoriasis, drug reactions, mites and dry skin. This type of itch is often treated with antihistamines and other drugs that alter the immune reaction.
Neuropathic itch is caused by damage to the nervous system. It is usually accompanied by sensations of numbness and tingling. This type of itch is seen after shingles, after stroke or burn injury, and in notalgia parasthetica (an area of itchy skin, usually on the back). It is treated with non-narcotic analgesics and capsaicin.
Neurogenic itch is seen in chronic liver and kidney disease in response to opioid neuropeptides. It is treated with narcotic and non-narcotic analgesics.
Psychogenic itch is induced in response to the chemicals serotonin and norepinephrine. These chemicals influence stress, depression and delusional parasitosis (a false belief of parasite infestation). Psychogenic itch is treated with antidepressants and antipsychotic medications.
An allergist / immunologist has advanced training and experience to identify what is triggering a persistent or reoccurring itch and to prescribe treatment.
This article has been reviewed by Andrew Moore, MD, FAAAAI