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For more than a decade, in blog posts and scientific papers and public talks, the psychologist Hal Herzog has questioned whether owning pets makes people happier and healthier.

It is a lonely quest, convincing people that puppies and kittens may not actually be terrific for their physical and mental health. “When I talk to people about this,” Herzog recently said, “nobody believes me.” A prominent professor at a major public university once described him as “a super curmudgeon” who is, in effect, “trying to prove that apple pie causes cancer.”

As a teenager in New Jersey in the 1960s, Herzog kept dogs and cats, as well as an iguana, a duck, and a boa constrictor named Boa. Now a professor emeritus at Western Carolina University, he insists he’s not out to smear anyone’s furry friends. In a blog post questioning the so-called pet effect, in 2012, Herzog included a photo of his cat, Tilly. “She makes my life better,” he wrote. “Please Don’t Blame The Messenger!”

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When Ina Chung, a Colorado mother, first fed packaged foods to her infant, she was careful to read the labels. Her daughter was allergic to peanuts, dairy, and eggs, so products containing those ingredients were out. So were foods with labels that said they may contain the allergens.

Chung felt like this last category suggested a clear risk that wasn’t worth taking. “I had heard that the ingredient labels were regulated. And so I thought that that included those statements,” said Chung. “Which was not true.”

Precautionary allergen labels like those that say "processed in a facility that uses milk" or "may contain fish" are meant to address the potential for cross-contact. For instance, a granola bar that doesn’t list peanuts as an ingredient could still say they may be included. And in the United States, these warnings are not regulated; companies can use whatever precautionary phrasing they choose on any product. Some don’t bother with any labels, even in facilities where unintended allergens slip in; others list allergens that may pose little risk. Robert Earl, vice president of regulatory affairs at Food Allergy Research & Education, or FARE, a nonprofit advocacy, research, and education group, has even seen such labels that include all nine common food allergens. “I would bet my bottom dollar not all of those allergens are even in the facility,” he said.