The skin reddens, silvery scales appear, itching and the urge to scratch increase, as do feelings of shame – for the approximately 1.3 million people in the UK who suffer from psoriasis, this is part of everyday life.

This chronic inflammatory skin disease manifests itself primarily in slightly raised red patches of skin covered with silvery scales. These so-called plaques often appear on the elbows, knees, scalp and behind the ears. In about half of psoriasis cases, fingernails and toenails also show changes. Around 20 percent of sufferers even develop psoriatic arthritis, which also causes inflammation of the tendons and joints.

In addition to the well-known problems – constant itching, sometimes open, painful skin areas and joint problems – another problem often takes a back seat: the considerable psychological stress caused by skin changes that are sometimes perceived as repulsive.

Many are ashamed of the conspicuous plaques, feel unattractive and worry about other people's reactions. In some cases, this even leads to those affected becoming increasingly withdrawn and isolated. The fact that people with psoriasis suffer from depression at an above-average rate is hardly surprising in this context.

Conventional medicine often reaches its limits here, which is why more and more psoriasis sufferers are looking for alternatives. Newer methods are increasingly focusing on the gut. But how is this supposed to work? Before examining this question in more detail, we should look at how psoriasis develops in the first place.

Psoriasis is a chronic autoimmune disease. It is caused by an overreaction of the immune system, which mistakenly recognises the body's own skin cells as a threat and attacks them. This leads to inflammation in the skin, which in turn causes new skin cells to be produced more quickly.

This is actually a good tactic, as it ensures faster healing in the event of injury. In the case of psoriasis, however, it means that the new skin cells are not only formed particularly quickly, but their "lifespan" is also extremely shortened.

While a normal, healthy skin cell undergoes a maturation process lasting around four weeks from the lower epidermal layer, where it is formed, to the skin surface, where it is finally keratinised and shed, this process only takes around four days in psoriasis.

The result: a kind of congestion of unfinished skin cells forms on the skin's surface, which stick together and lead to the notorious plaques.

Science has not yet been able to conclusively answer this question. Researchers currently assume that it is caused by a combination of genetic and environmental factors. It has been shown that children who have at least one parent with psoriasis have an increased risk of developing psoriasis themselves.

At the same time, however, a number of environmental and lifestyle triggers can be identified that also increase the likelihood of developing psoriasis. These include stress, various infectious diseases, diet, nicotine, body weight and much more.

In recent years, researchers have identified another particularly interesting potential "contributor" – one that you would not initially think of in connection with a skin condition. That would be the gut, or rather the microbiome. This refers to the totality of all living organisms, predominantly bacteria, that thrive in our gut.

However, diversity is not the only factor that is crucial for the gut to function properly: the total number of bacteria and their composition also play a decisive role.

If, for example, one strain is overrepresented or the number of another is reduced, the delicate balance of the microbiome is disrupted. Scientifically, this is referred to as dysbiosis. But what does this have to do with psoriasis? As it turns out, quite a lot!

A large number of studies have now been able to link the occurrence of psoriasis to an altered gut microbiome.

To get to the bottom of this, American professor J. U. Scher compared the microbiome of psoriasis sufferers with that of healthy test subjects and found clear differences: not only was the "psoriasis microbiome" significantly less diverse overall, it also lacked certain types of bacteria! These findings were confirmed in a further study by Francisco Codoñer, a professor in Valencia.

So, it seems clear that there is a link between the gut microbiome and the onset of psoriasis – but what does that mean for those affected?

Scientists G. Yin and J. F. Li investigated this question in 2019: they transferred the microbiome of a healthy person to a patient who had been suffering from severe psoriasis for ten years. In the following weeks, they examined both the psoriasis symptoms on the body and the impact of these skin problems on the patient's quality of life.

The groundbreaking finding: after only five weeks, both the externally visible symptoms and the patient's quality of life had improved dramatically! But how do you actually transfer a microbiome from one person to another?

To do this, the researchers resorted to a procedure that is by no means a modern invention: faecal transplantation. As early as the 4th century in China, doctors such as the famous physician Ge Hong used the intake of a healthy microbiome to treat various gastrointestinal complaints.

However, the administration was rather unappetising: Ge Hong treated patients by orally administering human stool! Although this procedure has been improved over the last millennium – nowadays, transplantation is either performed via a tube directly into the small intestine or by taking capsules – it can hardly be described as a pleasant treatment.

Although this form of therapy doesn't sound particularly appealing (even when it was given the poetic name "golden syrup" in the 16th century), it has been practised for a long time. Even today, the principle of stool transplantation is still practised in some cases – but fortunately in a far less unappetising way: the "foreign" stool is now administered via colonoscopy or capsules (up to 30 a day).

However, as these methods do not necessarily sound tempting and a stool transplant is not entirely without risks and, above all, involves high costs, it is only the method of choice in rare cases. So, is there perhaps an alternative?

A promising approach that is currently experiencing a real hype online lies in so-called probiotics.

Microculture preparations are preparations that contain live bacteria. The basic idea is similar to that of a stool transplant: the bacteria are supposed to colonise the gut, enrich the microbiome there and compensate for any dysbiosis that may be present.

Unlike a stool transplant, however, the bacteria for these preparations are cultivated in pharmaceutical facilities – a far cheaper, safer and, last but not least, more appetising idea. However, this raises the next problem: the incredible variety of products currently on the market. How is the layman supposed to separate the wheat from the chaff?