Itch (Pruritus) | Current Health Articles 2009

What is Itching?

Itching (Latin pruritus) is a skin sensation that provokes a desire to scratch (1). Itching occurs when certain substances produced by the body (e.g. biliary salts, histamine) or those coming from the outside (e.g. wool, nickel) irritate nerve endings in the skin.

Itching is not the same as tingling, or burning pain; they may all appear together though.

Mechanism of Itch

Stimuli that cause itch may originate from the skin, peripheral nerves, or central nervous system (spinal cord and brain). A common mediator of itch is histamine, released from mastocytes (special cells in the skin). This is why antihistamines may help in different types of itching.

Dermal Itch (Originating in the Skin)

Stimuli that can irritate the skin may be mechanical, thermal, chemical, orelectrical. If they irritate itch related nerve endings (itch receptors – pruriceptors), they cause itch, and if they irritate pain related nerve endings (pain receptors – nociceptors) they cause pain (2).

It seems that itch and pain mechanisms overlap considerably and may exclude each other to some level. For example: opioids (e.g. morphine) reduce pain, but may increase itch at the same time. On the other hand painful scratching may reduce itch (3). Information of skin irritation is conveyed via peripheral nerves through spinal cord into the brain where it is interpreted either as an itch or as a pain.

Itch receptors are present only in uppermost layer of the skin (epidermis) and mucous membranes of “body openings” (eyes, ears, nose, mouth and throat, anus, urethra, and genitalia). They are not present in muscles, joints and internal organs which therefore cannot itch (4).

Neuropathic Itch (Due to Nerve Damage)

Examples of neuropathic pain are brain tumors, multiple sclerosis, peripheral neuropathy (e.g. in diabetes), and nerve injury.

Neurogenic Itch

Neurogenic itch originates from central nervous system but not from damage of nerve tissue. It may be associated with opioids (analgesic substances) secreted from brain, or by synthetic opioids.

Psychogenic Itch

It is known that a person that doesn’t feel comfortable about something or is about saying something not really convincing…often rubs the bottom part of the nose… A feeling of itch may appear in psychological disorders like delusion of parasitosis or neurotic scratching.

Causes of Itch

Skin itch can be caused by sweating, dry skin, skin infections, allergies, liver or kidney disease, hormonal disorders, medications, psychological causes, etc. Read about causes of itchy skin. Seeing someone to scratch or even discussion about itch can cause itching sensation in some individuals; this is called contagious itch.

Localized Itch

Itch can be generalized (itching all over), or can affect only limited parts of skin or mucosa:

Scalp Itch
Facial Itch
Eyelid Itch
Eye Itch
Ear Itch
Nose Itch
Throat Itch
Neck Itch
Back Itch
Breast Itch
Under-Arm Itch
Arms and Hands Itch
Nail Itch
Itchy Limbs (Prurigo Nodularis)
Anal Itch
Vulvar Itch
Vaginal Itch
Jock Itch
Leg Itch
Foot Itch

Diagnosis of Itch

First, itch has to be distinguished from tingling and pain. Often a cause of itch can be determined from circumstances (e.g. insect bite, food allergy, medications/drugs…) or from skin changes like swelling, redness, discolorations, or rash.

When the cause of itch is not obvious, the following tests may be needed (9):

Measuring of body temperature (temperature is raised in many in infections and some cancers), and weight (weight loss occurs in malabsorption, some cancers, eating disorders, stress, etc.)
Body examination to find jaundice, rash, parasites, painful spots, areas of changed sensitivity etc.
Blood tests
- Red cells (decreased in anemia, increased in polycythemia)
- White cells (increased in various infections, leukemia, lymphomas)
- Sedimentation rate, CRP (elevated in some infections and in most malignancies)
- Glucose – blood sugar (elevated in diabetes)
- Urea (increased in kidney failure), blood urea nitrogen (BUN)
- Liver enzymes
- Thyroid and parathyroid hormones
- Vit A level
- Zinc level (zinc deficiency can cause itching and gastrointestinal problems)
- Toxic heavy metals (mercury, lead, aluminium, arsenic, bismuth, cadmium, etc.) (8)
Chest X-ray, if Hodgkin lymphoma is suspected
Abdominal ultrasound in suspected liver/gallbladder disease
Urine tests may reveal liver or kidney disease, elevated glucose levels, etc.
Stool tests may reveal intestinal parasites, hemoccult test may reveal intestinal bleeding (in Crohn’s disease, colorectal cancer)
In skin diseases, a skin scraping, or skin biopsy in which a small piece of skin is surgically removed and investigated under microscope may be needed. Skin redness, rash, blisters, swelling, bumps, or lumps are often associated with skin causes of itch, but rash can also appear in gut diseases like celiac disease, Crohn’s disease etc. It is important to remember that the presence of skin changes does not exclude the possibility of an underlying systemic cause, and the absence of a rash does not automatically mean that the underlying cause is a systemic disease. There might also be mixed causes of chronic pruritus
If an allergy is suspected, skin tests and blood tests (eosinophils – a type of white blood cell) may be done.
Diet trials may reveal food intolerances (lactose intolerance, fructose malabsorption, celiac disease), or allergies.
Temporarily discontinuation of medications may reveal drug side effects or allergies to certain drugs.

Treatment of Skin Itching

What to do to get rid of itching (9):

Avoid Scratching

Scratching can trigger additional itching, so resist to scratch, if possible.

Wash

Washing helps to relieve itching after:

An usual working day…
Excessive perspiration
Folliculitis
Contact with certain irritant substances like fiberglass (washing won’t help if dermatitis has already developed)

Avoid bathing in hot water, excessive use of soaps, and rough drying with towels.

Cool

Cold baths, light clothes, cool temperature at home and work relieves itching, while hot and humid environment aggravates it. Cool showers, and light bed clothes can relieve itch at night. Cold tap water, or compresses rinsed in cold water, ice cubs in plastic bag, or cooling lotions (calamine, pramoxine, menthol, eucalyptus, camphor) placed over the itchy skin area can help in:

bacterial skin infection like folliculitis
contact dermatitis
insect bite
allergies

Moist (Emollients, Moisturizers)

Therapy of itch due to dry skin bases on maintaining adequate skin moisture. Over-the-counter moisturizing cream (they should be odorless and colorless), applied right after bathing can help (6). Gently massaging itchy area may also bring some relief.

Antipruritics – Medications and Remedies Against Itch

Topical antipruritics (creams, sprays) are often available over-the-counter. Oral drugs are usually need prescription.

Antihistamines like diphenhydramine (Benadryl per mouth) help in allergic reactions. Antihistamines can cause drowsiness, so they shouldn’t be taken before driving. Antihistamines without sedation effect are loratidin and fexofenadine, available without prescription. Topical antihistamines should not be used as they may cause allergic dermatitis.
Corticosteroids: hydrocortisone topical cream in low (1%) concentration (to prevent thining of the skin) can reduce skin inflammation. Corticosteroids per mouth are used in heavy arthritis, multiple sclerosis, or other systemic inflammatory diseases.
Local anesthetics (benzocaine topical cream) may be used in intense itching, or burning pain.
Opioid-receptor antagonists (naloxone, butorphanol intranasal spray, naltrexone tablets) may be used in sever pruritus, e.g. in kidney or liver disease.
Tricyclic antidepressants as Doxepin or amitriptyline have antipruritic properties. Tetracyclic antidepressants such as mirtazepine and selective serotonin reuptake inhibitors (paroxetine, fluoxetine) may help in severe itch.
Adstringents (drying agents). Burrow’s solution (containing aluminium acetate) shrinks vessels in the skin or mucous membranes thus reducing inflammation and itch. It may be used as a cold compress in inflammed swollen skin (e.g. in hives in poison ivy, cellulitis) or mucosal membranes e.g. to treat vulvar or vaginal itch.
Capsaicin ointment may help in intense localized itching like in nostalgia paresthetica (back itch), or in localized tingling.
Tacrolimus ointment can be prescribed in atopic dermatitis.
Crotamiton (Eurax) cream can be used to treat scabies.
Exchange resins such as cholestyramine bind bile salts in skin and thus help in relieving itch due to liver disease with cholestasis.
Chelating agents as EDTA bind heavy metals and may help in itch due to toxic metal intoxications.
Pramoxin is effective in rosacea.
Low protein diet may help in relieving itching in chronic renal failure
Cholestyramine and rifampin help in liver disease with bile flow obstruction. Cholestyramine was not proved effective in renal failure.
Aspirin may help in some non-allergic causes of pruritus. Aspirin shouldn’t be used to treat itch in children with viral diseases, since it can cause Reye’s syndrome - a rare but severe hepatic disorder.

Antimicrobials

In fungal, parasitic, or bacterial infections, antimicrobial ointments or soaps, or antibiotics by mouth or injection may be required. In some viral infections (Epstein-Barr, Herpes zoster, citomegalovirus…) acyclovir (or its variants) per mouth, or as ointments may help.

Phototherapy

Phototherapy using ultraviolet UV-B rays is effective in severe itching (renal failure, prurigo nodularis, atopic dermatitis, AIDS, and aquagenic pruritus). Psoralen plus ultraviolet A (PUVA) phototherapy may help in polycythemia.

Treat the Cause

The cause of the itchiness may be usually successfully treated in bacterial, and fungal infections, and parasites. Most kidney and hormonal disorders, and even several cancers can be successfully treated.

Wait and Prevent

Sometimes treatment of the cause is not possible, or not needed, so waiting that the disease heals by itself, and prevention of its re-occurrence is recommended. This may apply for:

Most viral skin infections
Staphylococcal or pseudomonas folliculitis
Viral hepatitis
Contact dermatitis
Allergies
Ciguatera poisoning

Itch Prevention

Measures to reduce possibility to get an itching condition include:

Showering or bathing regularly, washing hair at least once a weak, washing hands to avoid contracting skin staph infection or parasites, washing sportswear after each use, etc.
Avoiding hot humid environment
Avoiding alcohol, caffeine, spices that dilate skin vessels and thus heat the skin
Wearing light, lose clothes and underwear made by material that absorb sweat (e.g. cotton). Wool, rough natural materials like flax, and synthetic clothes may irritate the skin.
Using protective clothes when dealing with irritant substances (e.g. fiberglass, detergents), working on garden, walking through woods etc.
Protecting against wind and sun by using appropriate clothes and cremes.
Limit cosmetics

Scratching

Scratching can irritate the skin and lead to more itching. Vigorous scratching may cause deep scrapes in the skin. In some people, even gentle scratching causes raised, red streaks that can itch intensely. Prolonged scratching and rubbing can thicken and scar the skin. Fingernails, especially children’s, should be kept short to minimize abrasions from scratching. If the urge to scratch is irresistible, rubbing the skin with the palm rather than scratching is recommended.

Scratching an itch on one part of the body can cause itching sensation on another, obviously unrelated part of the body. This is called referred itch or Mitempfindung (7).

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