I’ve read that they are and aren’t depending on the context. [It’s been shown](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6025786/) that EM radiation from normal, every day use electronics can interfere with our bodies. [Apparently](https://www.popsci.com/what-are-antioxidants-good-bad-enough-too-much/), it’s not entirely obvious that free radicals are dangerous? Can someone break it down for me?
In: Biology
**Free Radicals**
Free radicals are atoms or molecules with one or more unpaired electrons (usually one, otherwise the unpaired electrons tend to pair up). For reasons that are beyond the scope of ELI5, electrons are much more stable when paired than when unpaired. The result is that:
* Anything with an unpaired electron is extremely reactive and tends to steal an electron from or donate one to whatever it hits first.
* Because almost everything it might hit has all its electrons paired up, whatever it hits will itself become a free radical – the first radical steals an electron from it or donates an electron to it, leaving it with one unpaired electron.
* The newly created radical then reacts with whatever it hits next, and this process will continue until one radical hits another and they recombine (known as the termination step).
* Worsening this situation, because radicals are so reactive, they can make bonds that are difficult to break by non-radical methods (and therefore make things that are difficult for cells to repair or dispose of).
So, yes, free radicals are dangerous. They are a major source of DNA damage in cells, along with other kinds of damage that are also important but that are probably less relevant here (because everything except DNA is replaceable and usually replaced relatively quickly). Outside of a biological context, they also played a key role in depleting the ozone layer back when that was a problem; CFCs got into the stratosphere and were then dissociated by UV light, releasing chlorine radicals that catalytically degraded ozone through basically the mechanism I described above.
Our cells have to deal with free radicals all the time. You may or may not be familiar with the fact that, in respiration, oxygen does not directly react with glucose; instead, a series of reactions that I won’t go into convert glucose (and some water) to carbon dioxide and [electrons and protons], and the electrons and protons are then delivered to oxygen one at a time to produce water, yielding the net equation of glucose + 6*oxygen –> 6*carbon dioxide + 6*water that you’re hopefully familiar with. This is important because the oxygen can sometimes escape before all four electrons have been added, producing superoxide (one electron added), hydrogen peroxide (two electrons added, not itself a radical but still fairly nasty and can produce radicals under certain circumstances), and hydroxyl radical (three electrons added). The upshot is that any cells that use oxygen (which is all multicellular life and a huge range of single-celled life) also have to deal with a constant trickle of free radicals (or *reactive oxygen species*, to capture the fact that peroxide is also involved but not strictly a radical).
Because of this, they’ve developed a whole host of mechanisms to deal with them. We have extremely effective enzymes for converting superoxide to peroxide and peroxide to water. AFAIK and as far as Wikipedia knows, we have no enzymes that can detoxify hydroxyl radical, but our cells contain antioxidant molecules in order to scavenge those and other radicals and reactive molecules.
**Free Radicals – Biological Functions**
Dangerous as free radicals are, they have certain properties that can make them useful. I am not an expert on the role of free radicals in biochemistry, so this is very unlikely to be all the roles they play, but their two uses that I’m aware of are:
* Signalling. Free radicals are very short-lived, with half-lives of at most seconds and sometimes nanoseconds (barring exceptions), and that makes them useful short-ranged signals. Nitric oxide, which is a free radical, is an extremely important signalling molecule in a wide variety of pathways, such as vasodilation (widening of blood vessels); it’s particularly good in this role because it’s very small (so diffuses fast) and can cross membranes. I believe other free radicals also have signalling roles, but nitric oxide is probably the best-known one.
* The respiratory burst in phagocytes.
Elaborating on that last point; many immune cells attack pathogens by phagocytosing them; swallowing them, essentially. However, swallowing a pathogen doesn’t kill it. Among the most important of the mechanisms immune cells use to actually kill the pathogens they phagocytose is the respiratory burst, a phenomenon in which they dramatically increase their production of reactive oxygen species along with several other radical and reactive species within the phagolysosome (the compartment containing the pathogen; initially a phagosome, becomes a phagolysosome after merging with one or more lysosomes).
This is important because more specific killing methods (like degradative enzymes) are easier to defeat; bacteria might make inhibitors for those enzymes, change their surfaces so they’re no longer recognized by the enzymes, cover themselves in a protective layer, and so on. Free radicals, however, have an effect remarkably similar to setting something on fire; you can mitigate the effects, but no matter what you do it’s still going to hurt.
An example of this being important; people who have a mutation that makes them unable to produce some or all of the radical species in the respiratory burst often suffer from significant immunodeficiencies. Defects in NADPH oxidase (makes superoxide) cause chronic granulomatous disease, for example.
**Summary**
TLDR: Free radicals are a major source of DNA damage (leading to cancer) and are also generally very dangerous molecules. However, they can be very important for certain functions, and if you were to ask a genie to make it so that there were never any free radicals in your body, you would probably die (though how quickly would depend on how exactly the genie interpreted “free radical”).
**On EM & Electronics**
I am not equipped to evaluate the quality of the evidence presented in the review you linked (especially not in the amount of time I’m willing to devote to this), and the effect of non-ionizing EM radiation on biological systems appears to be a moderately complex topic. However, I’d apply some skepticism to at least [the specific review](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6025786/) you cite. It didn’t take me a huge amount of time to find a reference which they cite as showing that non-ionizing radiation causes changes in skin expression of HSP (a stress response protein) but in fact states [the exact opposite](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1241383/) (reference 58), which makes me suspicious of the quality of the review as a whole.
In general, while I’m not familiar with this topic, my impression is that the current state of knowledge on low-frequency EM and biological systems is “the evidence is conflicting, there are a few somewhat plausible mechanisms by which it might do something and some studies that suggest that it does but also quite a few studies that suggest it doesn’t”. If anyone actually familiar with this subject happens to read this and feels like elaborating, that would be greatly appreciated!
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