What is Itch (Pruritus)?

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

Itch is not the same as tingling, or burning pain; they may sometimes 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 substance histamine is usually released from mastocytes (special cells in the skin) in itch. This is why antihistamines may help in different types of itch.

1. Dermal Itch (Originating in the Skin)

Stimuli that can irritate the skin may be mechanical, thermal, chemical, or electrical. 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), but not in the muscles, joints and internal organs, which therefore cannot itch (4).

2. Neuropathic Itch (Due to Nerve Damage)

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

3. Neurogenic Itch

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

4. Psychogenic Itch

It is known that a person who does not 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 also appear in psychological disorders, like delusion of parasitosis or neurotic scratching.

Causes of Itch

Skin itch can be caused by sweating, dry skin, infections, allergies, liver or kidney disease, hormonal disorders, medications, psychological causes, and so on (read more about causes of itchy skin). Seeing someone to scratch or even discussion about itch can cause itchy 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 the skin or mucosa:

Diagnosis of Itch

First, itch has to be distinguished from tingling and pain. Often a cause of itch can be determined from circumstances, like 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, and so on)
  • Body examination to find jaundice, rash, parasites, painful spots, areas of changed sensitivity, and other skin changes.
  • 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, and so on.
  • Stool tests may reveal intestinal parasites; hemoccult testmay reveal intestinal bleeding (in Crohn’s disease, colorectal cancer)
  • In skin diseases, a skin scraping, or skin biopsy, during which a small piece of skin is surgically removed and investigated under microscope may be required. 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 diseaseand others. It is important to remember that the presence of skin changes does not exclude the possibility of an underlying disease, and the absence of a rash does not exclude skin disorders. Besides that, two or more causes of chronic pruritus may exist at the same time.
  • 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):

1. Avoid Scratching

Scratching can cause more itch, so resist to scratch, if possible.

2. Wash

Washing helps to relieve itching after:

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

3. Cool

Cold baths, light clothes, cool temperature at home and work relieves itch, while hot and humid environment aggravates it. Cool showers and light bed clothes can relieve itch at night. Cold tap wateror 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

4. 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.

5. 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 should not 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 thinning 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, for example, 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 (like in hives in poison ivy, cellulitis) or mucosal membranes, for example, to treat vulvar or vaginal itch.
  • Capsaicin ointment may help in intense localized itch 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 caused by liver disease with cholestasis.
  • Chelating agents, like 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 itch 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 certain non-allergic causes of pruritus. Aspirin should not be used to treat itch in children with viral diseases, since it can cause Reye’s syndrome - a rare but severe hepatic disorder.

6. 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.

7. Phototherapy

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

8. Treat the Cause

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

9. Wait and Prevent

Sometimes treatment of the cause is not possible, or not necessary, so waiting that a 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
  • 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 (like cotton). Wool, rough natural materials like flax, and synthetic clothes may irritate the skin.
  • Using protective clothes when dealing with irritant substances, like fiberglass or detergents, working on garden, walking through woods
  • Protecting against wind and sun by using appropriate clothes and cremes
  • Limiting cosmetics

Scratching

Scratching can irritate the skin and aggravate itch. 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 in children, 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 itchy sensation on another, obviously unrelated part of the body. This is called referred itch or Mitempfindung (7).

References:

  1. Itching (pruritus) definition (cancer.gov)
  2. Prurireceptors (healthatoz.com)
  3. Antagonistic action of pain and itch stimuli (pubmed.gov)
  4. Mechanism of itch (iasp-pain.org)
  5. Medications for itchy skin (pubmed.gov)
  6. Remedies and medications for itchy skin (merck.com)
  7. Referred itch – Mitempfindung (content.karger.com)
  8. Toxic metals (osha.gov)
  9. Tests and treatment of generalized pruritus (clevelandclinicmeded.com)

Article reviewed by Dr. Greg. Last updated on August 3, 2013