Why do we itch? The reasons are many and varied. But what's becoming ever clearer is many who experience chronic itching due to skin conditions also shoulder a profound psychological burden no scratching can relieve.

While the nature of this link around conditions like eczema and psoriasis has been investigated before, scientists say we're still only beginning to understand how skin disorders, mental health problems, and quality of life all intersect.

"There are already studies showing evidence of a correlation between itch and mental health problems in general, and in specific skin disorders, but there is a lack of a cross-sectional study across chronic skin diseases," says dermatologist Florence J. Dalgard from Lund University in Sweden.

To help fill that gap, Dalgard and her team analysed data collected from thousands of dermatology patients with skin issues in 13 European countries, including the UK, France, Germany, Russia, and elsewhere.

In total, over 3,500 patients with varying skin diseases took part in the study, undergoing physical examinations and filling out a questionnaire which asked questions about their socio-economic background and experiences with itching, while also measuring symptoms of depression, anxiety, and suicidal ideation.

More than 1,300 people without skin conditions acted as a control group, self-reporting the same information.

When the research team analysed the responses, they found a number of associations between skin conditions, itching, mood disorders, and quality of life impairments.

In patients with skin conditions who reported itching, the prevalence of depression was 14.1 percent. This lowered to 5.7 percent in patients who didn't itch.

Controls without skin disorders who reported itching also had around a 6 percent prevalent of depression - while only 3.2 percent in the control group members who didn't have itching reported depression.

Anxiety bore a similar pattern, showing up in 21.4 percent of the patients with skin conditions and itching, and dropping to 12.3 percent in patients without itching, while approximately 8 percent of the controls reported anxiety.

The prevalence of suicidal ideation was higher in patients with itch (15.7 percent) than in patients without itch (9.1 percent); similarly, it was higher in controls with itch (18.6 percent) than controls without (8.6 percent).

Patients with itch further reported experiencing more negative life events than the patients without itch did (38.2 percent compared to 32.4 percent respectively), and the patients who experienced itching were also likely to experience more economic problems.

While the team acknowledge their data can prove nothing about causation one way or the other (and submit that mental health suffering could potentially induce itch to some degree), they suggest it is much more likely that skin diseases are the cause of itching, which then leads to mental health effects.

"Speculative reasons for this correlation is that itch correlates with skin inflammation and skin inflammation induces serotonin network in the brain leading to depression and anxiety," the authors write in their paper.

While more research is needed to explore the hypothesis, for now at least, the link between itching and depression looks more firmly established than ever.

And that, the researchers say, should be reflected in how we treat patients with skin conditions – with a multidisciplinary team of physicians to help support these people, and everything they may be dealing with.

At the same time, preventative programs might be able to play a role in helping to ease itching and maybe reducing the development of the serious psychological symptoms that appear to stem from it.

"Our findings demonstrate that the presence of itch in dermatological patients is significantly associated with clinical depression, suicidal ideation and stress," the researchers conclude.

"The study reveals that itch contributes substantially to the psychological burden of dermatological patients and confirms the multi-dimensional suffering of dermatological patients with itch."

The findings are reported in Journal of Investigative Dermatology.