Today, some scientists think [that] germs can teach our bodies how to fight back against tumors. Dr. John Timmerman, a cancer immunotherapy expert at UCLA's Jonsson Cancer Center, says this revolution has produced the most exciting sets of compounds in cancer immunology." New studies are revealing that certain cancers may be reduced by exposure to disease-causing bacteria and viruses. The studies also imply that our cleaner, infection-free lifestyles may be contributing to the rise in certain cancers over the last 50 years, scientists say, because they make the immune system weaker or less mature. Germs cause disease but may also fortify the body, a notion summed up in a 2006 report by a team of Canadian researchers as "whatever does not kill me makes me stronger." In the 1980s, dermatologists began noticing that patients with severe acne, which is caused by another type of bacterium, have reduced rates of skin cancer, lymphoma and leukemia. According to a paper by Dr. Mohammad Namazi at the Shiraz University of Medical Sciences in Iran, studies showed that these bacteria, when injected into animals, appear to stimulate the immune system and shrink tumors. In reports published in the last two years, Harvey Checkoway, a University of Washington epidemiologist, has found that female cotton workers in Shanghai have a 40% to 60% lower risk of lung, breast, and pancreas cancer than other factory workers. Other recent studies by Giuseppe Mastrangelo at the University of Padua in Italy found that dairy farmers exposed to high levels of manure dust are up to five times less likely to develop lung cancer than their colleagues who work in open fields.