Psychogenic pruritus is a common manifestation of chronic anxiety, usually a localized itch, especially in the anogenital area.

The condition is often managed with drugs including H1-antihistamines, tricyclic antidepressants, tetracyclic antidepressants, selective serotonin reuptake inhibitors, antipsychotics, or benzodiazepines.

The exact mechanism of the condition is unknown, though some studies have suggested the itching occurs in response to increased fibrinolytic activity in the skin. Later studies indicated inappropriate activation of the sympathetic nervous system may play a part.

Approximately 280 million people globally, 4% of the population, have difficulty with itchiness. This is comparable to the 2–3% of the population suffering from psoriasis.

The name is derived from Latin: aquagenic, meaning water-induced, and pruritus, meaning itch.

Drug-induced pruritus is itchiness of the skin caused by medication, a pruritic reaction that is generalized.

Itch (also known as pruritus) is a that causes the desire or reflex to scratch. Itch has resisted many attempts to classify it as any one type of sensory experience. Modern science has shown that itch has many similarities to pain, and while both are unpleasant sensory experiences, their behavioral response patterns are different. Pain creates a withdrawal reflex, whereas itch leads to a scratch reflex.

Unmyelinated nerve fibers for itch and pain both originate in the skin; however, information for them is conveyed centrally in two distinct systems that both use the same nerve bundle and spinothalamic tract.

If a specific cause for pruritus ani is found it is classified as "secondary pruritus ani". If a specific cause is NOT found it is classified as "idiopathic pruritus ani". The irritation can be caused by intestinal parasites, anal perspiration, frequent liquid stools, diarrhea, residual stool deposits, or the escape of small amounts of stool as a result of incontinence or flatulence. Another cause is yeast infection or candidiasis. Some diseases increase the possibility of yeast infections, such as diabetes mellitus or HIV infection. Treatment with antibiotics can bring about a disturbance of the natural balance of intestinal flora, and lead to perianal thrush, a yeast infection affecting the anus. Psoriasis also can be present in the anal area and cause irritation. Abnormal passageways (fistulas) from the small intestine or colon to the skin surrounding the anus can form as a result of disease (such as Crohn's disease), acting as channels which may allow leakage of irritating fluids to the anal area. Other problems that can contribute to anal itching include pinworms, hemorrhoids, tears of the anal skin near the mucocutaneous junction (fissures), and skin tags (abnormal local growth of anal skin). Aside from diseases relative to the condition, a common view suggests that the initial cause of the itch may have passed, and that the illness is in fact prolonged by what is known as an itch-scratch-itch cycle. It states that scratching the itch encourages the release of inflammatory chemicals, which worsen redness, intensifies itchiness and increases the area covered by dry skin, thereby causing a snowball effect.

Some authorities describe “psychogenic pruritus” or "functional itch disorder", where psychological factors may contribute to awareness of itching.

Ingestion of helminth (worm) "Enterobius vermicularis" (pinworm, or threadworm) eggs leads to enterobiasis, indicative of severe itching around the anus from migration of gravid females from the bowel. Severe cases of enterobiasis result in hemorrhage and eczema.

One way to treat xerotic eczema is to avoid ing the affected area and to apply anti-itch or moisturizing lotion frequently.

A study published in 2005 found positive results from soaking the affected area in water for twenty minutes and then applying mid- to high-strength corticosteroid ointment.

Aquadynia is a variant of aquagenic pruritus, and characterized by a widespread burning pain that lasts 15 to 45 minutes after water exposure.

Uremic pruritus (also known as uraemic pruritus or renal pruritus) is caused by chronic kidney failure and is the most common internal systemic cause of itching.

Nalfurafine, an orally-administered, centrally-acting κ-opioid receptor agonist, is approved to treat the condition in Japan.

Xerotic eczema (also known as "Eczema craquelé", "Pruritus hiemalis", "Asteatotic eczema", "Winter itch", "Desiccation dermatitis," and "Winter eczema") is a form of eczema that is characterized by changes that occur when skin becomes abnormally dry, itchy, and cracked. Lower legs tend to be especially affected, although it can appear in the underarm area as well.

Xerotic eczema is common in elderly people, though it is not uncommon for people in their 20s. It can appear in red, bumpy, pimple-like irritations. Shaving can cause it to become inflamed.

A common cause of lick granuloma appears to be psychological, related to stress, anxiety, separation anxiety, boredom, or compulsiveness. Lick granulomas are especially seen in large active dogs left alone for long periods of time. It is often considered to be a form of canine obsessive-compulsive disorder.

But other less common causes include bacterial or fungal infections, trauma causing nerve damage, allergies, or joint disease. Hot spots may also lead to the formation of lick granulomas.

Many large breed dogs appear to be predisposed, as well as golden retrievers and other bird dogs. Most of the dogs with the condition are over five years of age. Seventy percent of the time it occurs on one of the dog's left legs. Arthritic and mobility problems in older dogs give them more time to lick and over-groom themselves.

Frequent formations of lick granulomas in the same area due to the constant licking will cause hardening, callous formation, hair loss (the hair may stop growing back), and hyperpigmentation to that area. The condition becomes a vicious cycle – erosion of the skin from licking leads to pain and itching, which leads to more licking. Lick granulomas sometimes become infected with bacteria, causing abscessed areas or fistulous tracts (furuncles).

Pruritus ani is the irritation of the skin at the exit of the rectum, known as the anus, causing the desire to scratch. The intensity of anal itching increases from moisture, pressure, and rubbing caused by clothing and sitting. At worst, anal itching causes intolerable discomfort that often is accompanied by burning and soreness. It is estimated that up to 5% of the population of the United States experiences this type of discomfort daily.

Biliary pruritus is caused by chronic liver disease with obstructive jaundice, characterized by a severe generalized itchy sensation.

Treatment of the primary cause, if known, is essential.

In psychogenic cases, dealing with psychological factors is most important. Factors should be identified such as being left alone all day, being confined, and changes in the household. Correction of these causes may include increased walks, avoiding confinement, and more interaction in the home. Some veterinarians have proposed that diet can affect compulsive behaviors in dogs.

Drugs may be used until behavior modification has had time to take effect. Antidepressants are most commonly used, including doxepin, amitriptyline, fluoxetine, and clomipramine. If the psychological factors are not corrected, the pet will usually relapse after the drugs are discontinued. Endorphin blockers such as naltrexone can be used to reduce addiction to licking, or endorphin substitutes such as hydrocodone may decrease the urge to lick.

The animal should be tested for allergies, and treated accordingly if positive (fatty acids, antihistamines, hypoallergic diet, etc.). It may also be necessary to check thyroid levels, as hypothyroidism seems to play a role in some cases, particularly in black Labrador retrievers; thyroid medication often will resolve the problem if it's due to hypothyroidism.

Generally, lichen nitidus is asymptomatic and self-limited; therefore, no treatment is required. However, if persistent pruritus is present, or the appearance “...interferes with daily activities or outlook...” topical glucocorticoids may be tried. If the disease process is symptomatic, generalized and extensive, oral glucocorticoids may be indicated. Other reported treatments include PUVA, UVA/UVB phototherapy, astemizole, acitretin, and etretinate.

When appears with sun/humidity; air conditioning (cool dry air) reduces swelling and discomfort.

Riehl melanosis is a form of contact dermatitis, beginning with pruritus, erythema, and pigmentation that gradually spreads which, after reaching a certain extent, becomes stationary. The pathogenesis of Riehl melanosis is believed to be sun exposure following the use of some perfumes or creams (a photocontact dermatitis).

HIV-associated pruritus is a cutaneous condition, an itchiness of the skin, that occurs in up to 30% of HIV infected people, occurs when the T-cell count drops below 400 per cubic mm.

Adverse reactions to biologic agents, such as imatinib, occur in more than 80% of patients, and can be characterized by edema and pruritus without dermatitis.

Linear arrangements of these papules is common (referred to as a Koebner phenomenon), especially on the forearms, but may occasionally be grouped, though not confluent, on flexural areas. Generally, the initial lesions are localized, and remain so, to the chest, abdomen, glans penis, and flexor aspects of the upper extremities; however, less commonly, the disease process can (1) be strictly isolated to the palms and soles, presenting with many hyperkeratotic, yellow papules that may coalesce into plaques that fissure or “...sometimes a non-specific keratoderma resembling chronic eczema,” or (2) become more widespread, with papules widely distributed on the body—the extensor surfaces of the elbows, wrists, and hands, folds of the neck, submammary region in females, groin, thighs, ankles, and feet—and fusing into erythematous, minimally scaled plaques, with reddness that develops tints of violet, brown, and yellow.

The Mazzotti reaction, first described in 1948, is a symptom complex seen in patients after undergoing treatment of onchocerciasis with the medication diethylcarbamazine (DEC). Mazzotti reactions can be life-threatening, and are characterized by fever, urticaria, swollen and tender lymph nodes, tachycardia, hypotension, arthralgias, oedema, and abdominal pain that occur within seven days of treatment of microfilariasis. The Mazzotti reaction correlates with intensity of infection; however, there are probably multiple infection intensity-dependent mechanisms responsible for mediating this complex reaction.

The phenomenon is so common when DEC is used for the treatment of onchocerciasis that this drug is the basis of a skin patch test used to confirm that diagnosis. The drug patch is placed on the skin, and if the patient is infected with the microfilaria of "O. volvulus", localized pruritus and urticaria are seen at the application site.

A case of the Mazzotti reaction has been reported after presumptive treatment of schistosomiasis and strongyloidiasis with ivermectin, praziquantel and albendazole. The patient had complete resolution of symptoms after intravenous therapy with methylprednisolone.

Autoimmune estrogen dermatitis presents as a cyclic skin disorder, that may appear eczematous, papular, bullous, or urticarial. with pruritus typically present, skin eruptions that may be chronic but which are exacerbated premenstrually or occur immediately following menses.

Chronic and repetitive scratching, picking, or rubbing of the nodules may result in permanent changes to the skin, including nodular lichenification, hyperkeratosis, hyperpigmentation, and skin thickening. Unhealed, excoriated lesions are often scaly, crusted or scabbed. Many patients report a lack of wound healing even when medications relieve the itching and subsequent scratching.

Patients often:

- seek treatment during middle-age, although PN can occur at any age.

- have a history of chronic severe pruritus.

- have a significant medical history for unrelated conditions.

- suffer from liver or kidney dysfunctions.

- suffer secondary skin infections.

- have a personal or family history of atopic dermatitis.

- have other autoimmune disorders.

- have low vitamin D levels.

The cause of prurigo nodularis is unknown, although other conditions may induce PN. PN has been linked to Becker's nevus, linear IgA disease, an autoimmune condition, liver disease and T cells. Systemic pruritus has been linked to cholestasis, thyroid disease, polycythaemia rubra vera, uraemia, Hodgkins disease, HIV and other immunodeficiency diseases. Internal malignancies, liver failure, renal failure, and psychiatric illnesses have been considered to induce PN, although more recent research has refuted a psychiatric cause for PN. Patients report an ongoing battle to distinguish themselves from those with psychiatric disorders such as delusions of parasitosis and other psychiatric conditions.

Brachioradial pruritus (BRP) is a localized pruritus of the dorsolateral aspect of the arm. BRP is an enigmatic condition with a controversial cause; some authors consider BRP to be a photodermatosis, whereas other authors attribute BRP to compression of cervical nerve roots.

BRP may be attributed to a neuropathy, such as chronic cervical radiculopathy. The possibility of an underlying neuropathy should be considered in the evaluation and treatment of all patients with BRP.

The main cause of BRP is not known, but there is evidence to suggest that BRP may arise in the nervous system. Cervical spine disease may be an important contributing factor.

Patients with BRP may have underlying cervical spine pathology. Whether this association is causal or coincidental remains to be determined.

There is controversy regarding the cause of brachioradial pruritus: is it caused by a nerve compression in the cervical spine or is it caused by a prolonged exposure to sunlight?

In many patients, itching of the arms or shoulders is seasonal. Some patients reported neck pain.

BRP can be linked to the thyroid.