The neurobiology of itch is complex and still not well understood, says UCI Health dermatologist Dr. Linda T. Doan.
Most people have felt the annoyance of an itchy feeling on their skin.
It triggers an urge to scratch and can have many possible causes.
Some people have even experienced such severe itching that it has caused insomnia, mood disorders, suicidal thoughts and affected personal relationships.
“Itch is hugely disruptive to the lives of those who suffer from it,” says UCI Health dermatologist Dr. Linda T. Doan.
“Can you imagine night after night of not being able to sleep because you’re too itchy?”
The mystery of itch
Doan says pruritis, the medical term for the itching sensation that causes a desire to scratch, is a complicated condition.
“The neurobiology of itch is complex and is still not well understood,” she notes.
“Itching is similar to pain in the sense that both are considered noxious or unpleasant stimuli.”
In both pain and itch, sensory nerves communicate through the spinal cord to various parts of the brain. But in pain, Doan says, we withdraw. With an itch, we scratch in response.
The root cause of that sensation can come from the skin, the spinal cord or the brain itself.
Itch with a rash
Itch with a rash tends to be more straightforward to identify and treat. Such conditions include hives, bug bites, eczema or psoriasis.
“The primary cause of itch involving a rash is usually something affecting the skin itself, so we are able to directly address those causes,” Doan says.
Relief may be as simple as applying cool compresses, moisturizers or taking warm baths.
There are also a variety of topical anti-itch creams or ointments, some containing topical steroids to stop swelling or inflammation, or other medications with antihistamines to tamp down an allergic reaction.
Itch without a rash
An itching sensation without any rash can be more challenging to treat because it’s harder to identify an underlying cause.
“In these cases, it can be an issue of the sensory nerves or the central nervous system itself,” says Doan. “It can also be a systemic problem — there are certain systemic disorders that can cause itch.”
Those include:
- Medication side effects
- Thyroid disease
- Kidney dysfunction
- Bile duct obstruction
- Certain cancer types
Other causes of itch
Conditions such as multiple sclerosis that involve nerve damage also can cause an itching sensation that scratching cannot relieve.
Itching can also afflict older adults, a condition called pruritus of the elderly.
“In these cases, there’s nothing wrong with the skin,” Doan explains. “It is thought that it’s due to age-related dysfunction of the nerves in one’s skin.”
Trauma to the spinal cord — from a car accident, for example — can also cause the body’s sensory nerve pathways to misfire and create a localized itch.
“The nerve will send a message to your brain that you’re itchy in one spot even though there’s nothing there stimulating the ends of those nerves.”
Doan also notes that seeing another person scratching themselves can bring on what’s called “contagious itching” and makes one feel compelled to scratch, too.
“We don’t really understand it, but it’s really interesting,” she says.
“A lot of work still needs to be done to understand the various pathways of itch, and how the brain processes it.”
Seeking treatment
While some itching can be addressed and treated at home, Doan suggests seeing a doctor when itching:
- Does not significantly improve with the conservative measures mentioned above (moisturization, topical antihistamine creams or oral antihistamines for itching associated with an allergic response, or topical over-the-counter steroids) within two weeks
- Is sudden and unexplainable
- Is associated with a rash that you don't recognize, including rashes that blister
- Is severe enough to cause insomnia and disrupts your daily activities
- Is associated with other symptoms such as weight loss, fever and night sweats
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