Allergic contact dermatitis is a delayed type IV hypersensitivity skin reaction to external stimuli. Patterns of dermatitis depend on allergen exposure and patch testing is the gold standard to identify causal agents. The American Contact Dermatitis Society identifies an “Allergen of the Year” in order to highlight facts about particular allergens, which may range from showing increasing prevalence of disease, to documenting low levels of relevant allergic reactions. This article reviews the allergens of the year from 2000 to 2020 with an emphasis on clinical relevance. Categories of allergens include adhesives, dyes, medications, metals, preservatives, rubber accelerators, surfactants, and other skin care product ingredients.