Big Tissue wants you to believe bathroom hand dryers spread disease. Here's what science says.

Welcome to Dear Julia, a column where readers submit everyday health questions. Which over-the-counter painkillers work best? Will intermittent fasting help you lose weight? Julia Belluz sifts through the research and consults experts in the field to figure out how science can help us live happier and healthier lives.

Dear Julia: Can hand dryers in bathrooms make people sick?

There's no doubt public bathrooms can be scary places, and there's no shortage of studies that seem to stoke our worst toilet fears. There's science that shows flushing a toilet can spray a mist of poo into the air, that public bathroom surfaces — door handles and soap dispensers — are covered in bacteria from our urine and feces, and that certain types of hand dryers are particularly effective at dispersing all these germs.

But while everyone agrees that thoroughly washing your hands is hugely important for avoiding disease, there's actually little agreement on the cleanest method for drying your hands afterward.

When I started to look at the evidence, I found it was mixed and plagued by conflicts of interest. One recent study, which carried frightening images like the one below and found that hand dryers increased the spread of bacteria, happened to be funded by the European Tissue Symposium, a trade association that represents tissue paper producers in Europe.

Another study, which touted the Dyson Airblade "for reducing bacterial transfer" was paid for by Dyson, the manufacturer of the Airblade, that sleek yellow and gray device that you stick your hands into rather than under for drying.

An independent randomized control trial, which compared the levels of bacteria left on washed hands after using four different drying methods (cloth towels, paper towels, hand dryer, spontaneous evaporation), found no difference in the germ levels in any group.

So just to sum up: A study finding tissues were more hygienic than air dryers was funded by "Big Tissue." A study finding warm-air dryers reduced bacteria spread was funded by "Big Hand Dryer." A high-quality independent study found no difference among the drying methods.

Ultimately, the best way to get a sense of what the sum of the evidence shows is with a systematic review. Good review articles take many studies and weigh them based on their relative strengths and weaknesses to come to more fully supported conclusions.

Thankfully, the Mayo Clinic Proceedings published one on the hygiene effects of different hand-drying methods in 2012. In it, the researchers noted that the evidence was mixed and very limited. But they concluded that "from a hygiene standpoint, paper towels are superior to air dryers," and recommended them for places where "hygiene is paramount" since towels generally seemed to leave fewer bacteria on the hands compared with hand dryers.

They suggested a couple of potential reasons for this difference: Friction can help "dislodge microorganisms from the skin surface," and perhaps dryers leave bugs lingering in a way rubbing hands dry with paper towels doesn't. And hand dryers can circulate and disperse germs in dirty bathrooms, sucking contaminated air in — and if they don't have proper filters — blowing it back on to the hands, chest, and face.

"On the basis of our review," the researchers wrote, "drying hands thoroughly with single-use, disposable paper towels is the preferred method of hand drying in terms of hand hygiene."

But wait, do hand dryers make people sick?

Importantly, unlike poor hand washing, there are no studies that specifically implicate hand dryers in the spread of disease. And while it's theoretically possible that a person could get infected by a virus that's sprayed out through a hand dryer, one must put the threat hand dryers pose into context. Are they really adding that much of a disease risk compared to the germ-infested door handles and sink faucets that people touch in the hand washing process?

Catherine Makison Booth, a senior scientist in the chemical and biological risks unit of the UK government, also pointed out that while it's important to keep in mind that the evidence is still pretty preliminary, "the limiting factor here regarding hand hygiene is a human one."

In other words, if people simply washed their hands properly — and only a tiny minority do — how they've dried them wouldn't matter as much. "Good hand washing practice is the key issue for me here above anything else," she summed up.

If you lean toward hypochondria, you may want to consider paper towels in your next washroom visit. If not, just wash your hands thoroughly and move on.

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