Itching

Definition

Itching (pruritus) is a sensation on the skin which makes you want to scratch. Itching may be local or generalised (affecting the whole body). Four types of itch are known according to the site of origin: 

  • Localised – due to local irritation;
  • Neuropathic – problems with nerves to the skin area;
  • Neurogenic – originating in the brain; and
  • Psychogenic – due to a psychological problem.

In all cases, the sensation of itch involves the release of chemicals like histamine in the skin, and/or the processing of nerve signals in the brain. The signals for itch and pain are carried by the same nerve fibres. 

Causes

Local factors are common causes of itch, such as:

  • Insect bites & stings,
  • Dry skin,
  • Irritants like soaps, perfumes and fabrics,
  • Skin infections like impetigo and fungal infections,
  • Skin disorders like pityriais, psoriasis, seborrhoiec dermatitis and urticaria,
  • Parasitic infection like lice and worms, and
  • Sunburn.

Causes of generalised itch include:

  • Diseases with rashes like chickenpox,
  • Allergies,
  • Lichen planus,
  • Liver disease with jaundice,
  • Iron deficiency anaemia,
  • Kidney failure (uraemia),
  • Others like leukaemia, thyroid disorders, diabetes and polycythaemia,
  • Drug reactions, and
  • Pregnancy.
  •  

Diagnosis

The diagnosis is obvious, but the cause may need investigating. A detailed history of onset, drug use and other symptoms should indicate a cause, but confirmatory tests may be needed. 

Blood tests for allergies and infections are useful; chest X-ray may show enlarged glands, and a skin biopsy may give the answer. 

Treatment

Because sensations of pain and itch share the same nerve fibres, scratching the affected area, causing mild pain, can act as a counter-irritant. However, excessive scratching can release even more histamine, making matters worse, and may also predispose to skin infections. 

Avoid known irritants, such as fabrics or contact allergens (like soaps). Avoid sun exposure, which can trigger or aggravate itch.

Underlying medical conditions contributing to itch (like kidney disease) are managed in their own right.

Topical relief may be had by moisturisers and steroid creams.

Systemic treatment by non-sedating antihistamines is effective. Gabapentin may be tried in uraemic patients who have not responded to other methods.

(Dr AG Hall)

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