Peanut allergy belongs to one of the most severe food allergies. So far 12 peanut allergens have been registered by the IUIS Allergen Nomenclature Subcommittee. The different peanut allergens and factors that contribute to allergenicity are described herein. Peanut contains several class I food allergens (especially Ara h 1, 2, 3) that are stable against heat denaturation and proteolytic digestion and represent storage proteins. These allergens are often associated with severe allergic reactions. Additionally, peanut contains class II food allergens (Ara h 5 and 8), where the IgE reactivity is caused by cross reactions to inhalant allergens. These allergens are mostly associated with mild to moderate allergic reactions. However, the severity of the symptoms may change by involvement of additional factors. The peanut matrix consists to about 50 % of lipids, and allergen-lipid associations have been shown for several peanut allergens. Further factors influencing allergenicity depend on the peanut variety, geographical differences and alterations in food processing. Finally, the physiological function of allergens and the mechanisms by which they interact with the immune system are further modulating factors. Thus, the specific allergen structure, matrix, genetic variations, geographic alterations and further augmentation factors are important parameters that induce and influence allergenicity.