Itching - Causes and Symptoms

Definition

Itching is a symptom that can cause significant discomfort; if intense, it causes the reflex or irrepressible desire to scratch, which in turn predisposes to inflammation and excoriations, to which secondary infections of the injured tissues may overlap.

There are numerous chemical mediators and different mechanisms that contribute to induce, transmit and maintain this sensation. Histamine, for example, is one of the most significant mediators: it is synthesized and stored in cutaneous mast cells and is released in response to various stimuli.

The itching can be triggered by different stimuli: a light touch, a vibration or contact with wool fibers. It can also be located in limited or generalized areas.

Many primitive skin diseases cause itching. The most frequent causes include dryness of the skin (xerosis), the bite of an insect, atopic dermatitis (eczema), contact dermatitis (secondary to contact with an allergen) and hives. The skin can be itchy even in the case of chronic lichen simplex, psoriasis, pediculosis, scabies and fungal skin infections (dermatophytosis).

Pruritus can also be a symptom of systemic diseases, with or without associated cutaneous manifestations. Among the most common causes are allergic reactions (to drugs, food, bites and stings), cholestasis, renal and hepatic failure. Less frequent systemic causes of pruritus include hyperthyroidism, hypothyroidism, diabetes, herpetiform dermatitis, iron deficiency anemia, Hodgkin's lymphoma and polycythemia vera. During gestation, itching may be due to three main conditions: pregnancy cholestasis, herpes gestationis and polymorphic dermatitis of pregnancy.

The itching can also be induced by the use of certain drugs, capable of triggering an allergic reaction or directly inducing itching through the release of histamine. Morphine, aspirin, barbiturates, penicillin, antifungal agents, chemotherapeutic agents and some intravenous contrast agents are the most common cause of this symptom.

Other causes of itching are neuropathic (related to disorders of the CNS or peripheral nervous system; eg multiple sclerosis and Herpes Zoster infection) and psychogenic (associated with psychiatric diseases; eg clinical depression, anxiety and various forms of psychosis).

The itching can be relieved by topical or systemic drugs, to be chosen based on the cause. Furthermore, it can be useful to limit the duration and frequency of baths (to be performed with warm water and delicate detergents), avoid potential irritants (eg tight or woolen clothes) and use emollients / moisturizers to restore the barrier function of the skin.