A number of years ago, a friend advised me to cover food being cooked or warmed in the microwave oven and to place a cup of water inside after use to absorb harmful waves. More recently, I read an article stating that using a microwave oven can trigger the development of cancer cells. If there is any truth in the latter, are my precautions sufficient? M.Z.S., Jerusalem Prof. Siegal Sadetzki, director of the information center and director of the cancer epidemiology and radiation unit at the Gertner Institute, Sheba Medical Center, Tel Hashomer, answers: Microwave ovens heat and cook food using microwaves, which are non-ionizing waves like radiowaves. This causes movement of the food molecules and causes them to heat up. The oven, when the door is closed, comprises a Faraday cage, an enclosure used to block electromagnetic fields that is named for physicist Michael Faraday. The door of the microwave is made of glass, but it is shielded by a tangle of iron so the radiation does not exit. As long as the device is functioning properly, with no gaps between the door and the frame and no holes in the iron, its use and being nearby are safe. In general, the answer to your question of whether non-ionizing radiation is dangerous to health hasn't been decided by scientists. One of the main research fields in this area is looking at any risk of developing cancer. In 2011, a working group of the International Agency for Cancer Research said that there is evidence of a higher risk for gliomas (brain cancers) and benign growths in the auditory nerve in people who use cellphones very frequently and hold them close to the head. But the evidence is not enough to reach conclusions about causality. As for other types of cancer and occupational and environmental exposure to these waves, the group listed radiowaves as B2, meaning that it is a “possible cause of human cancer.” Our guiding principle regarded non-ionizing radiation is preventive caution – taking simple measures to reduce exposure to the minimum. Thus today, it is recommended to keep the cellphone 50 to 100 centimeters from your head. Regarding the question of whether to put a glass of water in a microwave before or after using it and covering food during use, this prevents food from dirtying the inside and has no connection to exposure to radiation. A glass of water has no effect either during or after use, as a properly working microwave imprisons the rays inside the device and during operation, it will reduce the level of heating of the food. I am a new immigrant from Holland, but I have been reading the health and science articles in The Jerusalem Post for many years. I would like to know why the Health Ministry allows doctors to prescribe Micropirin 75 (aspirin) to thin patients' blood. I know from reports in Holland that this medicine causes big blue spots on arms and legs, often developing into long-term sores. Having settled in Israel in January of last year, I continue to take for this purpose what I was prescribed in Holland, Ascal 38 mg. (carbasalate calcium) and I have always had good results, but it is not sold here. I wonder why the Israeli Health Ministry does not allow the import the Dutch Ascal, which may be somewhat more expensive, instead of using Micropirin, which causes difficulties. M.L.K., Herzliya Prof. Eyal Schwartzberg, head of the Health Ministry's pharmaceutical and enforcement division, replies: Ascal is not a blood thinner but an analgesic that belongs to the group of NSAIDs (anti-inflammatory painkillers). What you describe is a possible side effect of any brand of aspirin. The Dutch drug is not registered in Israel and is not known to us (there are many drugs that are not registered here or imported to Israel). You should return to the doctor to report the symptoms as well as to consider other treatment alternatives available in Israel. If no other alternative is found or if you want the Dutch drug, it can be imported privately or institutionally by your health fund under Regulation 29. The Health Ministry is the regulator and responsible for approving drugs; it does not import them. The health fund of which you are a member is responsible for providing medications or alternatives that you need. Rx for Readers welcomes queries from readers about medical problems. Experts will answer those we find most interesting. Write Rx for Readers, The Jerusalem Post, POB 81, Jerusalem 9100002, fax your question to Judy Siegel-Itzkovich at (02) 538-9527, or email it to jsiegel@ jpost.com, giving your initials, age and place of residence.