Abstract: Modified allergens having reduced allergenicity compared to corresponding native allergenic material, wherein all or a part of the primary amine groups of the lysine and arginine residues of the allergenic molecules are functionalized and the modified allergens have the structure wherein R and R2 are independently selected from H, C1-C5 alkyl, phenyl, phenyl substituted in ortho, meta, or para with a hydroxy, C1-C4 alkoxy, halogen, amino, alkylamino, dialkylamino, mercapto, C1-C4 alkylmercapto group; X represents O, S, or NR3, where R3 is H, alkyl with 1-6 carbon atoms, phenyl, or CN; R1 represents H, alkyl with 1-8 carbon atoms, phenyl or arylalkyl with up to 8 carbon atoms, or alkyl containing a heterocyclic ring; prot represents the protein residue of the allergen; n is the number of functionalized arginine groups and ranges between 1 and the number of arginine groups present in the allergen; m is the number of functionalized lysine groups and ranges between 1 and the number of lysine groups present in