Merck Manual

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Julia Benedetti

, MD, Harvard Medical School

Reviewed/Revised Jan 2024
Topic Resources

Itching is a symptom that can cause significant discomfort and is one of the most common reasons for consultation with a dermatologist. Itching leads to scratching, which can cause inflammation, skin degradation, and possible secondary infection. The skin can become lichenified, scaly, and excoriated.

Pathophysiology of Itching

Itch can be prompted by diverse stimuli, including light touch, vibration, and wool fibers. There are a number of chemical mediators as well as different mechanisms by which the sensation of itch occurs. Specific peripheral sensory neurons mediate the itch sensation. These neurons are distinct from those that respond to light touch or pain; they contain a receptor, MrgA3, the stimulation of which causes the sensation of itching.


Histamine is the well-known mediator. It is synthesized and stored in mast cells in the skin and is released in response to various stimuli. Other mediators (eg, neuropeptides) can either cause the release of histamine or act as pruritogens themselves, thus explaining why antihistamines ameliorate some cases of itching and not others. Opioids have a central pruritic action as well as stimulating the peripherally mediated histamine itch.


There are 3 mechanisms of itch:

Intense itching stimulates vigorous scratching, which in turn can cause secondary skin conditions (eg, inflammation, excoriation, infection), which can lead to more itching through disruption of the skin barrier. Although scratching can temporarily reduce the sensation of itch by activating inhibitory neuronal circuits, it also leads to amplification of itching at the level of the brain, exacerbating the itch–scratch cycle.

Etiology of Itching

Itching can be a symptom of a primary skin disease or a systemic disease. Also, drugs and medications can cause itching (see table ).

Skin disorders

Systemic disorders

In systemic disorders, itching may occur with or without skin lesions. However, when itching is prominent without any identifiable skin lesions, systemic disorders, medications, and drugs should be considered more strongly. Systemic disorders are less often a cause of itching than skin disorders, but some of the more common causes include



Evaluation of Itching


History of present illness should determine onset of itching, initial location, course, duration, patterns of itching (eg, nocturnal or diurnal, intermittent or persistent, seasonal variation), and whether any rash is present. A careful medication history should be obtained including both prescription and over-the-counter medications with particular attention paid to recently started medications. The patient's use of moisturizers and other topicals (eg, hydrocortisone, diphenhydramine) should be reviewed. History should include any factors that make the itching better or worse.

Review of systems should seek symptoms of causative disorders, including

Past medical history should identify known causative disorders (eg, renal disease, cholestatic disorder, cancer being treated with chemotherapy) and the patient’s emotional state. Social history should focus on family members with similar itching and skin symptoms (eg, scabies, pediculosis); relationship of itching to occupation or exposures to plants, animals, or chemicals; and history of recent travel.

Physical examination

Physical examination begins with a review of clinical appearance for signs of jaundice, weight loss or gain, and fatigue. Close examination of the skin should be done, taking note of presence, morphology, extent, and distribution of lesions. Cutaneous examination also should make note of signs of secondary infection (eg, erythema, swelling, warmth, yellow or honey-colored crusting).

The examination should make note of significant adenopathy suggestive of cancer. Abdominal examination should focus on organomegaly, masses, and tenderness (cholestatic disorder or cancer). Neurologic examination should focus on weakness, spasticity, or numbness (multiple sclerosis).

Red flags

The following findings are of particular concern:

  • Constitutional symptoms of weight loss, fatigue, and night sweats

  • Extremity weakness, numbness, or tingling

  • Abdominal pain and jaundice

  • Urinary frequency, excessive thirst, and weight loss

Interpretation of findings

Generalized itching that begins shortly after use of a medication or exposure to a substance (eg, IV contrast) is likely caused by that agent. Localized itching (often with rash) that occurs in the area of contact with a substance is likely caused by that substance. However, many systemic allergies can be difficult to identify because patients typically have consumed multiple different foods and have been in contact with many substances before developing itching. Similarly, identifying a drug cause in a patient taking several medications may be difficult. Sometimes the patient has been taking the offending medication for months or even years before developing a reaction.

If an etiology is not immediately obvious, the appearance and location of skin lesions can suggest a diagnosis (see table ).

In the minority of patients in whom no skin lesions are evident, a systemic disorder should be considered. Some disorders that cause itching are readily apparent on evaluation (eg, chronic kidney disease, cholestatic jaundice). Other systemic disorders that cause itching are suggested by findings (see table ). Rarely, itching is the first manifestation of significant systemic disorders (eg, polycythemia vera Polycythemia Vera Polycythemia vera is a chronic myeloproliferative neoplasm characterized by an increase in morphologically normal red cells (its hallmark), but also white cells and platelets. Ten to 15% of... read more , certain cancers, hyperthyroidism Hyperthyroidism Hyperthyroidism is characterized by hypermetabolism and elevated serum levels of free thyroid hormones. Symptoms include palpitations, fatigue, weight loss, heat intolerance, anxiety, and tremor... read more Hyperthyroidism ).


Many dermatologic disorders are diagnosed clinically. However, when itching is accompanied by discrete skin lesions of uncertain etiology, biopsy Skin Biopsy Diagnostic tests are indicated when the cause of a skin lesion or disease is not obvious from history and physical examination alone. These include Patch testing Biopsy Scrapings Examination... read more Skin Biopsy can be appropriate.

When an allergic reaction is suspected but the substance is unknown, skin testing (either prick or patch testing Diagnosis Diagnosis depending on suspected etiology) is often done.

When a systemic disorder is suspected, testing is directed by the suspected cause and usually involves complete blood count; liver, renal, and thyroid function measurements; and appropriate evaluation for underlying cancer.

Treatment of Itching

Any underlying disorder is treated. Supportive treatment involves the following (see also table ):

  • Local skin care

  • Topical treatment

  • Systemic treatment

Skin care

Itching due to any cause benefits from use of cool or lukewarm (instead of hot) water when bathing, mild or moisturizing soap, limited bathing duration and frequency, frequent lubrication, humidification of dry air, and avoidance of irritating clothing. Avoidance of contact irritants (eg, wool clothing) also may be helpful.

Topical treatment

Topical medications may help localized itching. Options include lotions or creams that contain camphor and/or menthol, pramoxine, capsaicin, or corticosteroids. Corticosteroids are effective in relieving itch caused by inflammation but should be avoided for conditions that have no evidence of inflammation.

Topical benzocaine, diphenhydramine, and doxepin should be avoided because they may sensitize the skin.

Systemic treatment

Systemic medications are indicated for generalized itching or local itching resistant to topical agents. Antihistamines, most notably hydroxyzine, are effective, especially for nocturnal itch, and are most commonly used. Sedating antihistamines must be used cautiously in older adults during the day because they can lead to falls; newer nonsedating antihistamines such as loratadine, fexofenadine, and cetirizine can be useful for daytime itch. Other medications include doxepin (typically taken at night due to high level of sedation), cholestyramine (for renal failure, cholestasis, and polycythemia vera), opioid antagonists such as naltrexone (for biliary pruritus), and possibly gabapentin (for uremic pruritus).

Physical agents that may be effective for itching include ultraviolet phototherapy.


Geriatrics Essentials: Itching

Age-related changes in the immune system and in nerve fibers may contribute to the high prevalence of itch in older adults.

Xerotic eczema is very common among older adults. It is especially likely if itching is primarily on the lower extremities.

Severe, diffuse itching in older adults should raise concern for cancer, especially if another etiology is not immediately apparent.

When treating older adults, sedation can be a significant problem with antihistamines, so dose reduction may be appropriate. Use of nonsedating antihistamines during the day and sedating antihistamines at night, liberal use of topical ointments and corticosteroids (when appropriate), and consideration of ultraviolet phototherapy can help avoid the complications of sedation.

Key Points

  • Itching is usually a symptom of a skin disorder or systemic allergic reaction but can result from a systemic disorder.

  • If skin lesions are not evident, systemic causes should be investigated.

  • Skin care (eg, limiting bathing, avoiding irritants, moisturizing regularly, humidifying environment) should be observed.

  • Symptoms can be relieved by topical or systemic medications.

Drugs Mentioned In This Article

Drug Name Select Trade
ARYMO ER, Astramorph PF, Avinza, DepoDur, Duramorph PF, Infumorph, Kadian, MITIGO, MORPHABOND, MS Contin, MSIR, Opium Tincture, Oramorph SR, RMS, Roxanol, Roxanol-T
A-Hydrocort, Ala-Cort, Ala-Scalp, Alkindi, Anucort-HC, Anumed-HC, Anusol HC, Aquaphor Children's Itch Relief, Aquaphor Itch Relief, Balneol for Her, Caldecort , Cetacort, Colocort , Cortaid, Cortaid Advanced, Cortaid Intensive Therapy, Cortaid Sensitive Skin, CortAlo, Cortef, Cortenema, Corticaine, Corticool, Cortifoam, Cortizone-10, Cortizone-10 Cooling Relief, Cortizone-10 External Itch Relief, Cortizone-10 Intensive Healing, Cortizone-10 Plus, Cortizone-10 Quick Shot, Cortizone-5 , Dermarest Dricort, Dermarest Eczema, Dermarest Itch Relief, Encort, First - Hydrocortisone, Gly-Cort , GRx HiCort, Hemmorex-HC, Hemorrhoidal-HC, Hemril , Hycort, Hydro Skin, Hydrocortisone in Absorbase, Hydrocortone, Hydroskin , Hydroxym, Hytone, Instacort, Lacticare HC, Locoid, Locoid Lipocream, MiCort-HC , Monistat Complete Care Instant Itch Relief Cream, Neosporin Eczema, NuCort , Nutracort, NuZon, Pandel, Penecort, Preparation H Hydrocortisone, Proctocort, Proctocream-HC, Procto-Kit, Procto-Med HC , Procto-Pak, Proctosert HC , Proctosol-HC, Proctozone-HC, Rectacort HC, Rectasol-HC, Rederm, Sarnol-HC, Scalacort, Scalpicin Anti-Itch, Solu-Cortef, Texacort, Tucks HC, Vagisil Anti-Itch, Walgreens Intensive Healing, Westcort
Aid to Sleep, Alka-Seltzer Plus Allergy, Aller-G-Time , Altaryl, Banophen , Benadryl, Benadryl Allergy, Benadryl Allergy Children's , Benadryl Allergy Dye Free, Benadryl Allergy Kapgel, Benadryl Allergy Quick Dissolve, Benadryl Allergy Ultratab, Benadryl Children's Allergy, Benadryl Children's Allergy Fastmelt, Benadryl Children's Perfect Measure, Benadryl Itch Stopping, Ben-Tann , Children's Allergy, Compoz Nighttime Sleep Aid, Diphedryl , DIPHEN, Diphen AF , Diphenhist, DiphenMax , Dytan, ElixSure Allergy, Genahist , Geri-Dryl, Hydramine, Itch Relief , M-Dryl, Nighttime Sleep Aid, Nytol, PediaCare Children's Allergy, PediaCare Nighttime Cough, PediaClear Children's Cough, PHARBEDRYL, Q-Dryl, Quenalin , Siladryl Allergy, Silphen , Simply Sleep , Sleep Tabs, Sleepinal, Sominex, Sominex Maximum Strength, Theraflu Multi-Symptom Strip, Triaminic Allergy Thin Strip, Triaminic Cough and Runny Nose Strip, Tusstat, Unisom, Uni-Tann, Valu-Dryl , Vanamine PD, Vicks Qlearquil Nighttime Allergy Relief, Vicks ZzzQuil Nightime Sleep-Aid
Absorbine Jr, A-R Extreme, Arctic Relief, Arthritis Wonder, Aspercreme, Bengay Cold Therapy, BenGay Pain Relieving, BenGay Ultra Strength, BenGay Vanishing Scent, Bengay Zero Degrees, BiOFREEZE, BIOFREEZE Cold Therapy Pain Relieving, BIOFREEZE Overnight, BIOFREEZE Overnight Pain Relieving, BIOFREEZE Patch, BIOFREEZE PROFESSIONAL, Blue Gel, Cold & Hot Pain Relief Therapy, Eucerin Itch Relief, FLEXALL, Gold Bond, Icy Hot , Luden's, Medicated Topical Body, Mineral Ice, NitroVal Blue, PERFORM Pain Relieving, Therapy Ice, Vicks VapoDrop
Campho-Phenique Cold Sore Treatment for Scab Relief, Dermarest Eczema, DerMend, New-Skin Poison Ivy, Pramox Gel, Prax, Proctofoam, Sarna Sensitive, Tucks Fast Relief, Vagisil Anti-Itch
Arthricare for Women, Arthritis Pain Relieving, Capsimide, Capzasin-HP, Capzasin-P, Castiva Warming, Circatrix, DermacinRx Circata, DermacinRx Penetral, DiabetAid, Qutenza, Zostrix, Zostrix HP, Zostrix Maximum Strength, Zostrix Neuropathy
Advocate Pain Relief Stick, Americaine, Anbesol, Anbesol Baby , Anbesol Jr , Banadyne-3, Benzodent, Benz-O-Sthetic, Boil-Ease, Cepacol Sensations, Chloraseptic, Comfort Caine , Dry Socket Remedy, Freez Eez, HURRICAINE, HURRICAINE ONE, Little Remedies for Teethers, Monistat Care, Orabase, OraCoat CankerMelts, Orajel, Orajel Baby, Orajel Denture Plus, Orajel Maximum Strength, Orajel P.M., Orajel Protective, Orajel Severe Pain, Orajel Swabs, Orajel Ultra, Oral Pain Relief , Oticaine , Otocain, Outgro, Pinnacaine, Pro-Caine, RE Benzotic, Topex, Topicale Xtra, Zilactin-B
Prudoxin, Silenor, Sinequan, Zonalon
ANX , Atarax, Hyzine , Rezine, Vistaril, Vistaril Solution, Vistaril Suspension
Alavert, Allergy Relief, Claritin, Claritin 24 Hour, Claritin Chewable, Claritin Hives Relief, Claritin Liqui-Gel, Claritin RediTabs, Clear-Atadine , Dimetapp Children's Non-Drowsy Allergy, QlearQuil All Day & All Night Allergy Relief, Quality Choice Allergy Relief Non-Drowsy, Tavist ND
Allegra, Allegra Allergy 12 Hour , Allegra Allergy 24 Hour, Allegra Children's Allergy , Allegra Children's Allergy ODT, Allegra Hives, Allegra ODT, Allergy Relief, Children's Allergy
All Day Allergy , All Day Allergy Children's, Allergy Relief, Children's Allergy Relief, PediaCare Children's Allergy, Quzyttir, ZERVIATE, Zyrtec, Zyrtec Chewable, Zyrtec Children's, Zyrtec Children's Allergy , ZYRTEC Children's Dye Free, Zyrtec Children's Hives , Zyrtec Dissolve, ZYRTEC Dye Free, Zyrtec Hives Relief , Zyrtec Liquid Gel , Zyrtec Pre-Filled Spoons, Zyrtec Syrup
Locholest , Locholest Light, Prevalite , Questran, Questran Light
Depade, ReVia, Vivitrol
Active-PAC with Gabapentin, Gabarone , Gralise, Horizant, Neurontin
NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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