This is indeed true if, as in the case of any substance on this earth, it is used in unsafe amounts. Statements of this nature are unjustified and fraudulent when they are intended to misinform or alarm the public in a way that would indicate that ozone is unsafe under any circumstances. Ozone is created by the action of ultraviolet light or a strong electrical field on oxygen atoms. Ozone is lethal to almost all viruses, bacteria, fungus and cancer cells. The scientific literature is replete with articles proving these facts.
Ozone is formed in our atmosphere naturally by the effect of lightning on oxygen.
It is that wonderful sweet smell that you can detect after a summer storm. It is nature's method of cleansing our atmosphere of contamination. The poisonous ozone levels reported effecting our cities differs dramatically in that it represents the combining of the extensive overwhelming pollution with ozone insufficient to do the job. In 1931, Dr. Otto Warburg was awarded the Nobel Prize in biochemistry. Dr. Warburg demonstrated that the metabolism of a cancer cell was like that of a plant cell, which thrives on carbon dioxide and gives off oxygen as its waste product.