A novel hypothesis to explain why the prevalence of Behçet disease is highest in Turkey and other Silk Route countries

The pathogenesis of Behçet disease remains unknown although it is suggested that exposure to an infectious agent or an environmental antigen triggers an autoimmune response in genetically predisposed people. However, genetic predisposition does not fully explain why the disease is highest in Turkey and the ancient Silk Route countries. Here, detailed analysis of cultural, historical and medical data was conducted to identify environmental factor(s) that may be responsible for Behçet disease. These countries share common cultural habits such as hygiene practices including use of herbal products like rose water and Kolonya (Cologne) that may contain methanol of natural origin or from adulteration. Herbal distillates including rose water and essential oils have been used in Silk Route countries since ancient times. Studies from Iran (herbal distillates) and Turkey (Kolonya) have shown that methanol concentration in some of these products are high. Higher exposure to methanol in Turkey and other Silk Route countries, due to greater use of such products, may cause microbiome dysbiosis, immunotoxicity and other toxic effects leading to Behçet disease. Methanol, on its own or in conjunction with natural compounds from plants, may trigger inflammatory response directly or through dysbiosis of the microbiome. The hypothesis is supported by the fact methanol toxicity shares remarkable similarities with Behçet disease including neurological and ophthalmological effects (vision loss). The FDA (USA) warned the public not to use some brands of hand sanitisers due to contamination with methanol and recommends washing hands with soap and water. On the basis of the theory presented, an increase in the incidence of Behçet disease is predicted in coming years due to greater use of hygiene and herbal medicine products, during the COVID-19 pandemic, some of which may be contaminated with methanol. Research on this topic is needed and preventive steps taken to reduce exposure to methanol.