Intersections Between Allergic Diseases and Multiple Sclerosis: Mechanisms, Clinical Implications, and Hypersensitivity Reactions to Therapy

Multiple sclerosis (MS) and allergic diseases, traditionally considered immunologically opposing entities, may share pathogenic mechanisms rooted in immune dysregulation. While MS is predominantly mediated by Th1 and Th17 responses and allergies by Th2 responses, emerging evidence suggests overlapping immunological pathways, including the involvement of histamine, regulatory T cells, and innate lymphoid cells. This review synthesizes current knowledge on the epidemiological and immunopathological associations between MS and allergies. Epidemiological studies have yielded inconsistent results, with some suggesting a protective role for respiratory and food allergies against MS onset, while others find no significant correlation. Clinical studies indicate that food allergies in adults may be associated with increased MS inflammatory activity, whereas childhood atopy might exert a protective effect. In addition, we review hypersensitivity reactions to disease-modifying treatments for MS, detailing their immunological mechanisms, clinical presentation, and management, including desensitization protocols where applicable. Finally, we explore how treatments for allergic diseases—such as clemastine, allergen immunotherapy, montelukast, and omalizumab—may modulate MS pathophysiology, offering potential therapeutic synergies. Understanding the interplay between allergic and autoimmune processes is critical for optimizing care and developing innovative treatment approaches in MS.