The amino-acids susceptible to damage by oxidation caused by reactive oxygen species (ROS) are Histidine, Methionine, Cysteine, Tyrosine and Tryptophan. Generally, oxidation is classified into two categories: site-specific metal catalyzed oxidation and non-site specific oxidation.

Methionine and Tryptophan, to a weaker extent, are more susceptible to oxidation in non-site specific reaction. Methionine is dominantly sensitive to free ROS and Tryptophan to light induced oxidation. The extent of sensitivity lies on the solvent accessibility of the side chain and residues buried in the protein core are relatively less sensitive or need longer to react. Antibody oxidation can occur during antibody production, purification, formulation or storage and influence the biological activity and stability.