Xerosis: dry skin, frequently seen in the winter and also associated with older age, frequent bathing in hot showers or baths, and high-temperature and low-humidity environments. Other medical disorders
Diabetes mellitus, a group of metabolic diseases in which a person has high blood sugar
Hyperparathyroidism, overactivity of the parathyroid glands resulting in excess production of parathyroid hormone (PTH)
Iron deficiency anemia, a common anemia (low red blood cell or hemoglobin levels)
Cholestasis, where bile acids leaking into the serum activate peripheral opioid receptors, resulting in the characteristic generalized, severe itching
Malignancy or internal cancer, such as lymphoma or Hodgkins disease
Polycythemia, which can cause generalized itching due to increased histamines
Psychiatric disease ("psychogenic itch", as may be seen in delusional parasitosis)
Thyroid illness
Uraemia – the itching sensation this causes is known as uremic pruritus

Medication
Drugs (such as opioids) that activate histamine (H1) receptors or trigger histamine release
Chloroquine, a drug used in the treatment and prevention of malaria
Bile acid congeners such as obeticholic acid

Related to pregnancy
Gestational pemphigoid, a dermatosis of pregnancy
Intrahepatic cholestasis of pregnancy, a medical condition in which cholestasis occurs
Pruritic urticarial papules and plaques of pregnancy (PUPPP), a chronic hives-like rash

Other
Menopause, or changes in hormonal balances associated with aging
Terminal illness

Mechanism
Itch can originate in the peripheral nervous system (dermal or neuropathic) or in the central nervous system (neuropathic, neurogenic, or psychogenic). Dermal/pruritoceptive
Itch originating in the skin is known as pruritoceptive, and can be induced by a variety of stimuli, including mechanical, chemical, thermal, and electrical stimulation.
Crigler–Najjar syndrome is a rare inherited disorder affecting the metabolism of bilirubin, a chemical formed from the breakdown of the heme in red blood cells. The disorder results in a form of nonhemolytic jaundice, which results in high levels of unconjugated bilirubin and often leads to brain damage in infants. The disorder is inherited in an autosomal recessive manner. The annual incidence is estimated at 1 in 1,000,000.This syndrome is divided into types I and II, with the latter sometimes called Arias syndrome. These two types, along with Gilberts syndrome, Dubin–Johnson syndrome, and Rotor syndrome, make up the five known hereditary defects in bilirubin metabolism. Unlike Gilberts syndrome, only a few causes of Crigler–Najjar syndrome are known. Signs and symptoms
Jaundice 
Diarrhea
Vomiting
Fever
Confusion
Slurred speech
Difficulty swallowing
Change in gait, staggering frequent falling
Seizures

Cause
It is caused by abnormalities in the gene coding for uridine diphosphoglucuronate glucuronosyltransferase (UGT1A1). UGT1A1 normally catalyzes the conjugation of bilirubin and glucuronic acid within hepatocytes. Conjugated bilirubin is more water-soluble and is excreted in bile. Diagnosis
Type I
This is a very rare disease (estimated at 0.6–1.0 per million live births), and consanguinity increases the risk of this condition (other rare diseases may be present). Inheritance is autosomal recessive. Intense jaundice appears in the first days of life and persists thereafter. Type 1 is characterised by a serum bilirubin usually above 345 μmol/L [20 mg/dL] (range 310–755 μmol/L [18–44 mg/dL]) (whereas the reference range for total bilirubin is 2–14 μmol/L [0.1–0.8 mg/dL]). No UDP glucuronosyltransferase 1-A1 expression can be detected in the liver tissue.