Modern Wives' Tales: Give up the funk (We don’t want the funk)

I love onions and garlic (and other members of the allium family e.g. shallots, leeks, chives)!  However, I have a very sensitive nose (my youngest sister calls me a smelly person). I often have the problem of, having chopped an onion or garlic to prepare the evening meal, and having washed my hands thoroughly with soap and water after said preparation (and then again several more times throughout the evening), waking up the following morning with onion funk hands!

Note:  This chemistry will probably work well for other offensive smells due to thiols (e.g. skunk!) but I don't plan to go get sprayed by a skunk to find out.  If you have occasion to test this hypothesis, please let me know (and also, sorry you got sprayed by a skunk - that stinks!).

There are numerous Old Wives’ Tales that claim to remedy this situation.  The one that prompted this post was rubbing your hands with stainless steel.  Intrigued, I looked into the literature of onion funk before designing two experiments.

 All over the blogosphere it is well reported that onion (and other allium) funk comes from sulfur containing molecules.  This is where internet pseudo-science tends to diverge from real science.  We get all kinds of claims that the smell is due to sulfuric acid (which has, not so much a smell, but more of a choking feeling), hydrogen sulfide (smells like rotten eggs), and some other pretty wild ideas.  Not all sulfur containing molecules are created equal!

The molecules we are interested in belong to a class known as thiols.  One of the characteristics of thiols is having a smell like onions! Now we know we are on the right track.   It turns out, humans are really sensitive to smelling thiols – which is probably why they bother the likes of me so much.  To not smell the thiols from an onion we have to remove the thiols (hard to do adequately since we are so sensitive to them), or prevent our nose from being able to detect the existing molecules (preferably by preventing the reaction with our nose – not by destroying our sense of smell!).

We smell thiols because they have a particular motif ([a bunch of stuff]-S-H) that chemically reacts with odor receptors in our noses (likely by reacting with copper).  If we can chemically change the motif before it reaches the nose, it won’t be able to react with the odor receptors – we won’t smell it! 

Here is a list of the Old Wives’ recommendations for getting rid of funk, a likely explanation for why it made the list, and my hypothesis as to whether it would be effective as a defunkifier.

• Stainless Steel – People really swear by this one.  Stainless steel contains chromium, which, in some cases, binds thiols.  However, chromium that is exposed to air quickly reacts to form a thin “passivation” layer of chromium(III) oxide.  This molecule is very stable and will probably not react with thiols.  Any benefit from rubbing your hands with stainless steel is likely from the mechanical action of removing thiols (not reacting them) and could be obtained other ways (e.g. with soap and a nylon bristle brush).  It will also be difficult to get the object into the nooks and crannies (e.g. under the nails and cuticles), leaving stinky thiols to torment you. 

• Lemon juice – The major ingredient in lemon juice is citric acid.  There is no reason to suspect that this will react with the thiol.  It does leave a lasting and strong scent on your hands, perhaps masking onion odor for a time.

• Salt – There is no reason to suspect that salt (NaCl) reacts with the thiols.  Iodine (often added to table salt) will cause a reaction in thiols, but this may need to happen in the presence of a base – maybe if we make an iodized salt/baking soda combo.

• Vinegar – Vinegar is really just acetic acid.  It is smelly, so it might cover up the scent but it won’t change the thiols.

• Coffee – This one, surprisingly, might be more than just covering up the scent.  The scent of roasted coffee is caused by another thiol.  And thiols like to bind to each other.  So this might make the onion thiols not bind to your nose!  One might also try grapefruit juice for a similar reason.

• Toothpaste – this might be more than just a cover up (but my chemistry is not up to snuff enough to tell).  Toothpaste has a few compounds (e.g. a source of fluoride, baking soda or another base, hydrogen peroxide) that may cause thiols to change into another type of molecule.

• Hydrogen peroxide – I didn’t see this one in any sources online, but Hydrogen peroxide is known to change thiols into other molecules.  The only question is whether the concentration that is safe for skin contact would be a high enough concentration for defunkifing.  (We would have a similar problem with bleach.  Bleach would absolutely work to get rid of the smell (it is what we use in the lab to neutralize the odor of thiols) but you shouldn’t put it on your skin). 

Experiments

I devised two sets of experiments that could use information from each other to decide methods to test (e.g. if stainless steel worked in the first, I would test it with the second.  But if it didn’t work in the first, I wouldn’t bother trying it in the second). I chopped and then pulverized a large onion. 

For the first set of experiments, I dipped my hands in the onion slurry and then allowed the onion juice to dry on my skin (the things I do for science!) because anything less resulted in an onion funk that was easily removed by soap and water.  After letting the juice dry, I rinsed my hands with water and then used the treatment.  This way takes a while so I haven’t yet gotten through all the things that I need to try.   

For the other set of experiments, I soaked popsicle sticks in the onion slurry overnight.  I then rinsed the excess onion juices from the sticks and allowed them to dry.  I either soaked or coated the sticks in a paste of the treatment and let them sit for 1 hour.  I then rinsed the sticks and allowed to dry overnight (so that cover-up scents would dissipate).  I used a stick washed with hand soap as a control scent.

Results so far

Mostly, I have only convincingly determined methods that don’t diminish the onion scent more than soap and water.

For the first experiment: Stainless steel, baking soda alone, vinegar, and kosher salt were no better than soap and water.  Lemon juice showed promise because my hands smelled so lemony fresh after treatment, however it was the last treatment I did that evening and, though I went to bed with lemony fresh hands, I woke up with onion funk!  Because of these results, I did no further testing of these methods.  However, based on the results of the second set of experiments, there are some promising methods that I still need to try on hands.

For the second experiment:

I tried topical hydrogen peroxide, a paste of iodized salt, a paste of baking soda and iodized salt, toothpaste, and strongly brewed (and cooled) coffee.  All but the toothpaste and salt alone caused the onion funk to be undetectable.  The toothpaste stick smelled like minty onion – quite a bit more terrible than I would have imagined.  Please note: I use some cheapo toothpaste.  Maybe the good stuff has compounds that would work better.  But based on a cost analysis, everything else that is being tried is much cheaper per use so I wouldn’t recommend it.

I will try hydrogen peroxide, the baking soda/ iodized salt paste, and coffee on my hands in the next couple days and I will update.

Summary

No improvement over soap and water: stainless steel, baking soda alone, vinegar, kosher salt, iodized salt alone, and toothpaste.  Of these, only toothpaste had any (though probably weak) scientific basis for combating onion funk.

These show promise in the stick test, have decent scientific basis, and require further testing: topical hydrogen peroxide, baking soda/iodized salt paste, and cooled strong coffee.

P.S.  An ounce of prevention is worth a pound of cure.  My experiments (and intuition) suggest that onion funk becomes worse the longer you leave the onion juices on your skin.  If you either wear gloves or wash your hands immediately after handling the onion, you might be able to avoid this problem.