Could a little poison be a good thing?

Evidence is building for hormesis, the theory that suggests that moderate doses of bad things like radiation and toxins can improve health. Interestingly, much of the evidence has been around for a long time but it has been ignored because the focus was on proving the harm that toxins can cause and because low-dose effects are, by their nature, harder to identify so positive effects at low doses were typically discounted. Edward J. Calabrese of the University of Massachusetts at Amherst, however, has collected thousands of already published examples and is conducting original research of his own into hormesis. Other researchers are beginning to take notice. Hormesis is controversial, however, as you might imagine from this bombshell:

Calabrese suspects that in many cases, the benefits of hormesis may occur at levels higher than the recommended safe doses for humans.

Hormesis is a similar idea to the hygiene hypothesis (more here) which asserts that "reduced microbial exposure because of increased sanitation and cleaner lifestyles has facilitated the rise in asthma and allergic disease in the Western world." (The mechanisms of the two effects appear quite different, however.)