There is considerable oxidative stress on the tissue and glands close to a cellphone when in use and this may increase cancer risk, Israeli researchers say. Dr. Yaniv Hamzany of Tel Aviv University\'s Sackler Faculty of Medicine and the Otolaryngology Head and Neck Surgery Department at the Rabin Medical Center looked for clues in the saliva of cellphone users. Since the cellphone is placed close to the salivary gland when in use, he and fellow researchers Raphael Feinmesser, Thomas Shpitzer, Dr. Gideon Bahar and Rafi Nagler of Tel Aviv University and Dr. Moshe Gavish of the Technion in Haifa examined the saliva content of 20 heavy-user patients, defined as speaking on their phones for a minimum of 8 hours a month. Most participants speak much more, Hamzany said, as much as 30-40 hours a month. Their salivary content was compared to that of a control group, which consisted of deaf patients who either do not use a cellphone or use the device exclusively for sending text messages and other non-verbal functions. The study, published in the journal Antioxidants and Redox Signaling, found compared to the control group, the saliva of heavy users showed indications of higher oxidative stress -- a process that damages all aspects of a human cell, including DNA -- through the development of toxic peroxide and free radicals -- a major risk factor for cancer. Although the study didn\'t uncover a conclusive \"cause and effect\" relationship between cellular phone use and cancer, the research adds to the building evidence cellphone use might be harmful in the long term, the researchers said.