Has it been proven that being exposed to WiFi waves is harmful?
WIFi is non-ionising radiation and so has similar issues to other radiation using similar frequencies such as mobile telephones and microwave ovens. These produce heating effects. WiFi is not focused, so any impact should be very small and perhaps not measurable.
I am not aware of any health studies specifically on WiFi. There have been studies on mobile phones which has shown that while the phone is in use and held next to the head, there is small but measurable heating effect on human tissue. My guess is that it has less impact than standing at right angles to the Sun so one side of the head gets warmer faster than the other. Even then, these studies have produced no evidence that this has any health impact, positive or negative:
A large body of research exists, both epidemiological and experimental, in non-human animals and in humans, of which the majority shows no definite causative relationship between exposure to mobile phones and harmful biological effects in humans.
“When we have conducted measurements in schools, typical exposures from wi-fi are around 20 millionths of the international guideline levels of exposure to radiation. As a comparison, a child on a mobile phone receives up to 50 per cent of guideline levels. So a year sitting in a classroom near a wireless network is roughly equivalent to 20 minutes on a mobile. If wi-fi should be taken out of schools, then the mobile phone network should be shut down, too — and FM radio and TV, as the strength of their signals is similar to that from wi-fi in classrooms.”
The Sun does emit ionising radiation (ultra violet) and that has significant health effects such as sunburn, pigmentation changes and Vitamin D production. WiFi's impact, if anything, is nothing like this.
I am unaware of any research done on this specific question. The closest I've come across was this Dutch study, which states that there may be a connection between Wi-Fi transmissions and tree sickness. The research in itself was not sufficient to make that conclusion.
There are people who report a negative feeling when exposed to Wi-Fi, but those claims don't seem to stand up to proper double-blind testing, see for example:
Our study indicates that short-term exposure to mobile phone base station radiation does not affect the health and well-being of sensitive or control individuals.
Personally, based on my understanding of physics, I doubt that Wi-Fi radiation is harmful.
The explanations that follow are not 100% accurate or bullet-proof, but they should give the general idea.
Wi-Fi transmits at the 2.4 GHz frequency range; that's close to your microwave oven in the kitchen - and it has very much the same effect, that is it heats you up a little bit. Now, while that may be in theory a harmful effect, it should be noted that the change in temperature is much less than due to, say, having a little warmer weather (I'm cheating a little bit here).
But maybe we should look at it in a different way. This is a nice table from xkcd:
While admittedly not the most solid source of information, I do believe it can give the general notion. Look at the lowest dose of radiation that any research ever found to be linked with cancer (100 mSv), and compare how much radiation you are exposed to on your daily life.
The difference is quite large. So even with the (rather small) addition of radiation from Wi-Fi, you should be fine.
I did find one study about WiFi and trees. Conclusion translated to English from Dutch:
Wageningen University was commissioned by the municipality of Alphen aan den Rijn how the increasing number of sources of electromagnetic radiation, such as masts, could play a role in the deteriorating health of the trees. It was a growing cell the effect of radiation of known WiFi access points on small Esboompjes investigated.
The notes were exposed for more than three months to six sources of radiation with frequencies ranging from 2412 to 2472 MHz and a power of 100 mW EIRP
An association between the studied wifi radiation and the wide range of symptoms in adult trees can not be explicitly placed on the basis of the present study.
Also per this study by the California Department of Health Studies -- be advised, this is about EMFs from power lines, and I'm not clear how much stronger / weaker those are compared to radio frequency EMFs from cell phones and wifi:
On behalf of the California Public Utilities Commission (CPUC), three scientists who work for the California Department of Health Services (DHS) were asked to review the studies about possible health problems from electric and magnetic fields (EMFs) from power lines, wiring in buildings, some jobs, and appliances. The CPUC request for review did not include radio frequency EMFs from cell phones and radio towers. Reviewer 1, Vincent Delpizzo, Ph.D., is a physicist and epidemiologist; Reviewer 2, Raymond Richard Neutra, M.D., Dr.P.H., is a physician epidemiologist; and Reviewer 3, Geraldine Lee, Ph.D., is an epidemiologist with training in genetics. All three have published original research in the EMF area and have followed the field for many years. They were assisted in their reviews by DHS toxicologists, physicians, and epidemiologists.
The EMF Program’s policy analysis required each of the three DHS scientists to express in numbers their individual professional judgments that the range of added personal risks suggested by the epidemiological studies were “real.” They did this as a numerical “degree of certainty” on a scale of 0 to 100. For the conditions with the most suggestive evidence of EMF risk, the three scientists each came up with a graph that depicts their best judgments with a little “x” and the margin of uncertainty with a shaded bar: The differences in certainty between the three reviewers arises primarily from how sure they were that they could rule out study flaws or other explanatory agents and how much the evidence on one disease influenced certainty in the findings for other diseases.
As you can see from the "degree of certainty" from these professionals, the jury is very much out on this one.
In my opinion in the absence of even mildly compelling proof of danger, I don't think there is harm from reasonable, typical exposure to WiFi.
2017 Aug update 3 years down the road, this answer is still down the tube!! Feel free to ignore the facts. Here is one of the latest research https://link.springer.com/article/10.1007/s12020-015-0795-3, and http://time.com/4508432/what-is-wifi-radiation-cancer/
Original 2014 answer: Yes, an increasing body of research links WIFI with cancer and other harmful effects. Here is a study from 2013 dec that involved plant seeds:
In the experiment, they placed six trays in a room without any equipment and another six trays in a room next to two routers. Over 12 days many of the seedlings in the wifi room turned brown and died, whereas those in the others room thrived.
Also, a recent israeli study linked cell phone use with an increased presence of free radicals in saliva!
The results of the study published in Antioxidants and Redox Signaling showed the heavy mobile phone users had significantly greater saliva oxidative stress. “Our study indicates that mobile phone users experience considerable oxidative stress on proximal tissue as shown in the saliva, which mostly originates from the parotid glands,” the researchers concluded. “Oxidative stress is a potential contributor for the risk for developing cancer.”
One more quote for the downvoters from a recent event :D
the International Agency for Research on Cancer (IARC), a division of the World Health Organization (WHO), classified mobile phone use as a possible cause of cancer. After examining a body of evidence on mobile phone use, the IARC yesterday announced it will now classify mobile phone signals as ‘possibly carcinogenic’ due to some study results suggesting a link to some types of brain cancers.