One thing that I find that many people don't understand is the concept of risk.
Risk has a formal, mathematical definition: it is equal to the probability of exposure times the probability of harm. For example, an activity which is a commonplace occurrence (probability of exposure) and which, for those who participate in it, is very likely to cause injury or death (probability of harm) is considered to be highly risky. An example is riding a motorcycle without a helmet. Likewise, an activity for which both quantities are low -- such as eating a mango -- is a low-risk activity.
So far, easy. When it becomes less intuitive is when one of the quantities is low, and the other is high -- such as riding in an airplane. The probability of exposure is high (it's commonplace), but the probability of harm is extremely low (almost no one, of all the millions of people who fly daily, gets hurt doing it). The overall risk is therefore quite low -- but the times when injury and death occur are spectacular, leading most people to overestimate the risk wildly.
An additional complicating factor occurs when engaging in one behavior stops you from doing another -- in which case you need to consider the net risk. For example, if you're going to take a thousand-mile trip, and are undecided whether to fly or drive, the risk for flying is almost certainly lower than the risk for driving, so your net risk for the trip goes down by taking an airplane. (I realize that there are other factors that can influence the decision -- such as cost.)
The whole issue comes up because of an article sent to me by a reader of Skeptophilia. The article (here) is entitled "Twenty Things That Are More Dangerous To Children Than Lead Paint In Toys." It is a perfect example of a combination of pseudoscientific bunk, alarmism, and a complete misunderstanding of the concept of risk.
To take just a few of their examples of their "things that are dangerous:"
1) Mercury in dental amalgam. Never mind that hundreds of controlled, peer-reviewed studies have concluded that the amount of mercury absorbed by the body from dental fillings is far below the amount that would cause harm; this article repeats the tired old claim that the mercury in your fillings is "poisoning you." Odd, then, how many of us live long, healthy lives with mouths full of metal, isn't it? (Here's one nice debunking of this claim -- with references.)
2) Sunscreen. Contains many "poisonous chemicals," says the article, and yet we "slather it all over our children." First, given that the other options are getting sunburned, or avoiding the sun altogether, I think we can apply our concept of "net risk" here. Ever heard of malignant melanoma, folks? Second, the repeated use of the word "chemical" as something we should avoid is another ploy of the "holistic health" crowd, which cheerfully neglects the fact that we humans are really just a big bag o' chemicals already. (Another statement from the article is that children's clothes should not be "washed in chemicals." What, pray, should we wash them with, then?) "Natural" does not mean "good;" the naturalistic fallacy is rampant in these sorts of claims. I always get a laugh from food packages that say, "Made From All-Natural Ingredients." I wonder what food made from "All Unnatural Ingredients" would look like?
3) In the same vein, "synthetic vitamins" made the list. I'm sorry to inform you, Mr. and Ms. Holistic Health, but there is no difference between ascorbic acid (vitamin C) produced in a laboratory, and ascorbic acid extracted from oranges. The body can't tell the difference. There is no sorting station in your cells, looking at vitamin C molecules and saying, "Ooh, goodie! This is a nice, natural vitamin C molecule from an orange! Oh, YUK. This is a horrid, unnatural vitamin C molecule from a laboratory!"
4) Vaccines. This one torques the absolute hell out of me, largely because of a personal connection; my mother contracted polio as a child, and as a result limped for her entire adult life; and my grandfather's two sisters, both teenagers, died three days apart from measles. Died. All of this occurred in the days before vaccines, and yet these "Natural Health" people somehow claim that vaccines are harmful to your health. Yes, they often contain methyl mercury as a stabilizer (but like dental amalgam, the quantity is so low as to be insignificant to health), and every once in a while someone, somewhere will have an adverse reaction to a vaccine. But if you compare the actual risk of vaccination as compared to the actual risk of going unvaccinated, they are orders of magnitude apart. Vaccines have saved millions of lives -- and, to put not too fine a point on it -- if you are going to let unscientific bullshit like this persuade you not to vaccinate your children, you should be prosecuted for child endangerment.
Oh, and another thing; there is no connection between vaccines and autism. None. It has nothing to do with the "dumbed-down press" (direct quote from the article). Once again, we have peer-reviewed studies that have repeatedly found no correlation, and the wild, unsupported claims of a "natural health practitioner" who sits there shrieking that vaccines cause "severe neurological damage" (another quote).
Well, I know who I believe.
All of this is not meant to say that we shouldn't be careful about what we put into our bodies. Some of the things on the list (soda, fast food, and preserved meats such as hot dogs and bacon) clearly can have adverse effects if consumed in large quantities. (In fact, I find it curious that "dryer sheets" made the list, while "high fructose corn syrup" didn't. Compare the risk of type-2 diabetes from habitual overconsumption of sugar with recorded cases of dryer-sheet toxicity. Let me know what you find.)
So, that's today's rant. I'm off to consume my all-natural, chemical-free breakfast, and pray that the cumulative effects of my three dental fillings and years of vaccinations don't make me suddenly drop dead from "severe neurological damage."