Adults with atopic dermatitis have a 34% increased risk of developing new-onset inflammatory bowel disease compared with individuals who do not have AD.

Adults with atopic dermatitis (AD) have a 34% increased risk of developing new-onset inflammatory bowel disease (IBD) compared with individuals who do not have the skin condition, and children have a 44% increased risk, according to a new study from the Perelman School of Medicine at the University of Pennsylvania. 

Additionally, as the severity of AD increased, the risk of developing IBD rose. 

These findings should clear up ambiguity from previous research, especially among populations of children and between the different types of inflammatory bowel disease: ulcerative colitis and Crohn’s disease, the researchers noted.

The study appears in JAMA Dermatology

“It is imperative for clinicians to understand atopic dermatitis and the trajectory of our patients with it in order to provide the best standard of care,” says senior author Joel M Gelfand, MD, the James J. Leyden, M.D. Endowed Professor in Clinical Investigation in the department of Dermatology at Penn, in a news release.  “There are new and better treatments for AD today, and there will likely continue to be more. But providers have to understand how those treatments could impact other autoimmune diseases. For patients with AD and another autoimmune disease, some currently available medications can exacerbate symptoms of their other disease or can help treat two immune diseases at the same time.”

The Penn study included more than 1 million children (participants from under 1-year old to 18-years old) and adults with AD.

When looking at ulcerative colitis and Crohn’s disease separately, AD was not linked to higher ulcerative colitis in children unless the kids had severe AD. Children with AD, however, had a 54% to 97% increased relative risk of Crohn’s disease, and among children with severe AD, their risk was roughly five times higher. Results among adults were more straightforward. Adults with AD had a 32% increased relative risk of ulcerative colitis and a 36% increased relative risk of Crohn’s disease. Gelfand notes that the absolute extra risk of developing IBD in individuals with atopic dermatitis is still quite small, but the association is meaningful in better understanding health outcomes in AD. Moreover, since millions of people have atopic dermatitis, this small increase in risk spread among many people is likely important from a public health perspective.

Although Penn researchers did not look at the root cause of IBD linked to AD, they have strong hypotheses about the links.

“AD and IBD can cause changes in the microbiome, chronic inflammation, and the dysfunction in the skin and gut barrier respectively,” adds Dr. Gelfand, who is also the director of the Center for Clinical Sciences in Dermatology at Penn. “There are also specific cytokines, certain kinds of proteins, that play a role in immune system activity and that seem to be related to AD and IBD. For example, we think dysfunction of types of T cells common to both AD and IBD, could be the culprits. Those need to be explored further to uncover both what’s happening at a microscopic level and what proteins or structures could be targeted to treat one or both conditions.”