Scientists have shed new light on the maddening and often inexplicable problem of itchy skin.
Certain types of chronic itch, including one known as primary localised cutaneous amyloidosis (PLCA), are so serious they require medical treatment. And researchers at King's College London have found that in some cases the answer may be genetic.
Their study, published yesterday in the American Journal of Human Genetics, focused on the inherited form of this disease. The researchers found that a genetic disorder was caused by a defective copy of a skin cell gene called oncostatin M receptor-beta (OSMR).
In this case, cells with mutant forms of the gene do not respond as they should to signalling molecules. Stimulation by two particular molecules should trigger an anti-inflammatory response which prevents itchy skin, but when this does not happen, itchiness results.
Professor John McGrath, president of the European Society for Dermatological Research, said: "This work provides new insight into what can cause itchy skin. We now plan to look for abnormalities of this signalling pathway in other itchy skin disorders and, most importantly, to examine how we can develop new treatments for that most common of all skin symptoms – the itch."
Dr Yolande Harley, from the charity Action Medical Research, which funded the study, said: "This is the first discovery of a gene abnormality which directly causes itchy skin."
Itchiness has many causes we do know about, from insect bites, lice, the weather or surrounding environment, to more serious conditions such as leukaemia, or jaundice.
In many cases, such as with insect bites, an itch can be triggered by the release of chemicals including histamine from skin cells, stimulating specific nerve fibres which bring the sensation of an itch. Such chemicals can also be in everyday products, such as washing powder.
In some cases itchiness comes with psychological problems such as obsessive compulsive disorder. Eczema, for example, which affects hundreds of thousands of people in the UK, can be linked to stress. Itching can also be caused by a reaction to a medicine, or an allergy to many things, including cosmetics, fabrics or certain metals, such as nickel.