The most common chronic inflammatory skin disease is atopic dermatitis (AD), which has a significant effects on quality of life. Atopic allergic conditions (AACs) such as AD, asthma, hay fever, and food allergies have been surveyed in association with cancer risk in earlier studies. AACs indicate a intensified immune response and could contribute to distinguish and remove the malignant cells and as a result reduce the cancer risk. AACs are accompanied with frequent tissue inflammation, damage, and repair, which could possibly increase the risk of cancer. 

Several epidemiologic studies have assessed an association between AACs and colorectal cancer (CRC) risk. The exact nature of their association is still controversial and has been a topic of scientific debate with mixed results. 

A nationwide cohort study was conducted to evaluate the association between AD and risk of CRC. Data from Taiwans National Health Insurance Research Database was collected. 46,703 patients with AD and 186,812 sex, age, and index year-matched patients without AD were recognized from 2000 and 2008. 

Follow-up time was calculated from the entry date in the cohort till the incidence of a first CRC diagnosis, death, or the end of the observation period, whichever happened first. Subsequently, after multivariable adjustment, it was found that AD was associated with an increased risk of CRC. Most importantly, a significant positive association was found between AD and CRC risk and it was manifested in both men and women and in all age groups. 

Thus, the population-based cohort study concluded that AD was associated with an increased risk of CRC in an Asian population.

Source: Chou WY, Lai PY, Hu JM, et al. Association between atopic dermatitis and colorectal cancer risk: A nationwide cohort study. Medicine (Baltimore). 2020; 99(1):e18530.