The research on oxidative stress and in particular with regard to ascorbic acid (the dioxygenases are the only enzymes in humans that use ascorbate and the only reason it is essential) targets the dioxygenase enzyme family initially; but the pro-oxidant effect of ascorbate in the presence of 21% oxygen produces an abundance of oxygen radicals that induce genes and enzymes that terminate the growth and survival of the cell. Although research in this area is not sufficient, it is likely that all cells grown at 4-5% oxygen rather than at 21% will be more similar to the cells in vivo and thus make tissue culture a more relevant model for experimentation. Cells will be healthier, also grow faster and probably, in the case of non-immortalized cells, last for more passages. Unfortunately, immortalized cells which have been grown for many passages for decades may not resemble the cell of origin. This is another area of concern and must be considered in the interpretation of experimental data.