The Mighty Onion

A few days ago I received what could have been a life-changing email. The email claimed that my pantry was storing a vastly underused source of near-magical health power: raw onions.

What followed was a description of the astonishing medicinal powers of this bulb:

• Onions have amazing antibacterial and antiseptic properties.

• A raw onion placed next to a sick person could suck the sickness right out of them.

• Place a few cut up onions in your house and they will absorb all bacteria, saving your family from countless illnesses!

Just as I was thinking of the appropriate way to honor such a wondrous plant, I discovered that like all the best superheroes, the mighty onion had a dark side.

The email went on to reveal that since onions are such magnets for bacteria, eating an onion that is left out for too long can poison you. As if this weren’t shocking enough, in a scandalous showing of duplicity, the email warned that onions can even create deadly toxic bacteria of their own. Truly, with great antibacterial power comes great antibacterial responsibility.

Now I was in a real bind. Part of me wanted to throw out my penicillin and embrace this new antibacterial overlord. While another, more cautious part of me, worried about the toxic bacteria an unruly onion might unleash on my family.

Fortunately, as is often the case when I’m trying to evaluate the pros and cons of magical plants, science came to the rescue. Walk with me as I use science to analyze each of the amazing claims made by this potentially life-changing email:

Amazing Claim #1: Onions Have Antibacterial and Antiseptic Abilities

Science tells us that there is plenty of evidence to support this claim. Studies abound on the antibacterial properties of onion and its bulbous cousin, garlic. In fact, a recent study found that when combined with garlic and lime extracts, onions can help inhibit the growth of certain strains of E. coli which are resistant to conventional antibiotics.

Another study showed that onion powder, when combined with coconut extract, completely eliminated roundworm infection in mice after just 8 days of treatment. (Roundworms are a kind of parasite that mammals often get. If you’ve ever given your dog or cat deworming medicine, roundworms are one of the parasites the medicine is designed to kill.)

Both of these studies are quick to point out that these results don’t necessarily translate directly to human health, and you should of course consult your doctor before you decide to replace all of your antibiotics with onion powder and coconut extract.

Amazing Claims #2 and #3: Raw Onions Suck Disease Out of People and the Air

Since our email started out on such solid ground, I had high hopes for this claim of germ-sucking power. Unfortunately, while onion vapors have been shown to have some limited antimicrobial effects, placing an onion next to an infected person won’t cause bacteria to swarm out of them towards the onion.

Assuming that the bacteria wanted to become one with onion, the trouble is that while bacteria have some cool ways of getting around, spontaneous flying isn’t one of them. You could of course sneeze them onto the onion, but they can’t get over there on their own.

Ah, but what about breathing in those onion vapors? The study on onion vapor also noted that the effects of the vapor are limited by both time and temperature. After a few hours the onion vapors lose potency, even in the close confines of a petri dish. Their effect on someone sitting across the room would be pretty close to zero.

Amazing Claim #4: Onions Left Out Overnight Absorb So Many Bacteria, That They Turn Black and Poisonous!

Wait just a minute. How is it that onions are killing the bacteria and also giving them a new home? Well, they’re not. It turns out that the black slime you see growing on old onions isn’t bacteria at all. It’s a fungus called Aspergillus niger, more commonly known as Black mold. It can be found in most soils and grows on onions, garlics, peanuts, and a few other domestic crops. The jury is still out on just how bad it might be for people to eat it, but just like the warnings you’ve heard about yellow snow, eating slimy, black onions probably isn’t advisable.

Amazing Claim #5: Onions Create Toxic Bacteria

This claim harkens back to the age-old idea of spontaneous generation. This exciting theory concerning the origin of life led early researchers to believe that maggots are created by rotting meat, frogs pop out of pools of slime, and that anchovies came from sea foam.

Unfortunately for early Greek scientists and opportunistic merchants who hoped to save a fortune on pizza toppings by investing in sea foam, it turns out that this amazing theory was completely wrong. Not surprisingly, just like how frogs and anchovies come from other frogs and anchovies (respectively), bacteria come from other bacteria, not from vegetables. Sorry kids, no excuses for not eating your broccoli.

Conclusion

So where does this leave us? Do we honor the onion for its antimicrobial prowess, or shun it for its failure to be all that it claimed to be? Like most sensational claims, science has shown that the email I received was only loosely based on fact. Even though the onion isn’t the powerful cure-all that the email sender wanted us to believe, the onion redeems itself by managing to still contain some antimicrobial (and antioxidant) properties, making it a welcome addition to any pantry…until it turns black and slimy.

Resources

^{Watch how bacteria move – Visit the Microbiology Bytes video on motility}

^{Rahman et al.: Antibacterial activity of natural spices on multiple drug resistant Escherichia coli isolated from drinking water, Bangladesh. Annals of Clinical Microbiology and Antimicrobials 2011 10:10.}

^{Klimpel S, Abdel-Ghaffar F, Al-Rasheid KAS, Aksu G, Fischer K, Strassen B, Mehlhorn H (2011) The effects of different plant extracts on nematodes. Parasitol Res 108:1047–1054}

^{Lovell, T. H., Bactericidal Effects of Onion Vapors, Food Research., 1937, 2, 435L}

Onion image courtesy of Shutterstock.