A high-fat diet could aggravate skin diseases, such as psoriasis, by increasing the level of inflammatory cytokines in the skin, an A*STAR-led study finds.

Previous research has suggested that obesity is a trigger for psoriasis, a disease characterized by scaly, itches patches on the skin, thought to be associated with the immune system. So researchers from A*STAR, and colleagues in Japan, set out to explore the cause underlying the link between obesity and psoriasis.

Their study compared obese mice which had been fed a high-fat diet and lean mice on a normal diet. Both groups of mice were treated with a drug called imiquimod that can induce a psoriasis-like skin condition.

After 5 days of imiquimod treatment, they noticed that the obese mice, which had been fed the high-fat diet, exhibited significantly greater psoriasis-like symptoms than the mice on the normal diet.

To understand this, the team took a closer look at what was happening to the immune cells in the skin of the obese mice. They discovered that the cells lining the blood vessels in the skin were putting out chemical signals that caused an increase in a type of immune cell called a T cell. This T cell produced another chemical messenger called IL-17, which is associated with increased inflammation.

But the researchers still weren’t sure whether it was the obesity itself, or the high-fat diet that was responsible for the immune changes in the mice’s skin. To answer this, they repeated the treatment on mice that were genetically engineered to be obese even without the input of a high-fat diet. They found that these mice responded to the imiquimod treatment in a manner similar to that of lean, normal diet mice, which suggested that it was in fact the high-fat diet, and not the resulting obesity, that was contributing to higher levels of skin inflammation.

While most people know that a high-fat diet is associated with heart disease and diabetes, not many would think about its potential to cause skin disease, says Satoshi Nakamizo, from the Singapore Immunology Network and Institute of Medical Biology at A*STAR.

“A high-fat diet acts on a large blood vessel such as the heart, causing arteriosclerosis, but it also acts on small blood vessels of the skin and causes skin inflammation,” Nakamizo says. “Diet and weight management are important not only for systemic diseases but also for preventing skin diseases.”