Here's something you don't hear too often: Your house isn't dirty enough! According to the “cleanliness hypothesis,” asthma is on the rise in the United States and other rich countries because of overly protective parents who keep their houses too clean. That's right—dust, germs and even cats, according to a recent issue of The Lancet, may be our friends. Eliminating these toxins and irritants from our children's environment could be depriving them of a chance to build the immunity their systems need to conquer the world.

From the “sometimes it's better to reserve comment” file: an ophthalmologist at the University of Maryland Medical Center claims that a small number of men experienced ischemic optic neuropathy (and permanent vision loss) within minutes of taking a popular impotence drug (yes, that one). Only one of these men had other risk factors associated with the eye disorder. Researchers aren't sure how the vision loss occurs, but they believe the drug may change blood flow to the optic nerve, much the same way it does to other parts of the body.

“Hope for the best, but prepare for the worst.” That's probably good advice, at least according to data reported in Psychology Today suggesting that people who tend to look at the bright side are often disappointed. According to the study, presented at the American Psychological Society's annual meeting, setting up expectations is a protective behavior, and having low expectations means less chance for disappointment, even from a negative outcome. So much for the power of positive thinking.

More than genetics may determine who is susceptible to developing Alzheimer's disease. According to a study published in JAMA, the key suspect is vascular disease—high blood pressure, atherosclerosis and stroke. After comparing extremely poor market traders in Ibadan, Nigeria, whose diet consists mainly of vegetables, with blacks living in Indianapolis and eating a typical American diet, it was found that black Americans are more likely to develop dementia and Alzheimer's disease.

A caution flag has been tossed on the field over the purported health benefits of green tea, according to a study reported in New England Journal of Medicine. In 1984, researchers asked 26,311 residents of the Miyagi Prefecture in northern Japan (a country with high rates of stomach cancer) to complete a questionnaire regarding their health habits, including consumption of green tea. By 1992, 419 of the surveyed residents had been diagnosed with stomach cancer. People may continue drinking green tea, but perhaps for enjoyment only.

Studies of the health risks of cellular telephone use are ongoing. Early results suggest a variety of potential health problems, including cancer, pacemaker interference and effects of radiofrequency on the human body. In all of these studies, the most important health effect of cellular telephone use was found to be not in the potential risk of disease, but rather in the probability of motor vehicle collisions when drivers use a cell phone. The results of a study published in The Lancet indicate that the risk of collision is about four times greater when drivers are using a cell phone or soon after completing a call than when not using the gadgets. In addition, the use of “hands-free” cell phones doesn't seem to lessen the risk.