Thursday, May 10, 2012

Honey: A few studies I've found about its anti-microbial reputation

One of the things I see constantly about honey is that it is an anti-microbial, so let's take a look at the evidence for this concept. 

There are three features of honey that have been studied extensively for anti-bacterial properties - high osmolarity, acidity, and hydrogen peroxide production. This study found there were two phenolic acids - caffeic acid and ferulic acid - also had a role. 

High osmolarity means that there are many things dissolved in the solute and that things will want to go from a low osmolarity environment to the higher osmolarity environment. Honey has been tested to have a pH level from 3.4 to 6.1, with an average being around 3.9, so it's actually quite acidic. And honey contains an enzyme called glucose oxidase that will produce hydrogen peroxide when honey is exposed to oxygen, diluted, and brought to a more neutral pH, something that can happen when we put honey on a wound, for instance. It is destroyed when honey is exposed to heat and light.  Gluconic acid can behave as a chelating ingredient - meaning it binds with metal ions - and we know that chelating ingredients can help prevent microbial contamination in our products. 

Click here for a post on osmosis. Click here for a post on pH. Click here for more information on glucose oxidase and gluconic acid

Caffeic acid is a powerful anti-oxidant, out-performing almost every other anti-oxidant when tested. It is a possible fungicide, good anti-inflammatory, and may protect skin if applied after sun exposure. Ferulic acid can help reduce inflammation on our skin, and it works synergistically with other anti-oxidants to create a super anti-oxidant party that will help retard the rancidity of oils in your products and fight free radicals on your skin.

Click here for more information on mechanisms of rancidity and how anti-oxidants work

With all these great features, could we use honey to preserve our products? No. I've found nothing that shows that we could use honey to preserve anything we make. And I think there are a number of reasons...
  • Honey doesn't do well at higher temperatures and breaks down. If it breaks down, it's not going to be an effective preservative.  
  • Honey doesn't do well when diluted, and our water based products have quite a lot of water in them. (See the second abstract below). 
  • Honey will be in a less acidic product than it would normally be found. Our products tend to be in the 5.5 range. Although the neutralization of the honey's acidic pH is a good thing for releasing hydrogen peroxide, those enzymes are destroyed when exposed to heat and light, two things our products see regularly. 
  • You would have to use so much that it would be the main ingredient in the product, and it would feel very very sticky. 
I've found websites that say you can use honey as a preservative and they are simply wrong. I know this is a bold position to take, but I think I can say with confidence that any blog, website, or book suggesting that a teaspoon or two of honey will preserve your water based product is suggesting something dangerous to you. I have done more searches than I want to admit through Google, Google Scholar, and EBSCOhost at my university, and I can't find a single study that demonstrated that someone has successfully passed a challenge test while using honey as the sole preservative to preserve a bath and body, cosmetic, or toiletry product. I found one person claiming this in the comments in this post at Chemists' Corner, but you'll notice that he points out that he used a secondary preservative, so that's not evidence of honey being the sole preservative. And Anthony Dweck notes in this article that "Honey in its undiluted form is also a natural preservative and, indeed, there are many learnéd papers citing honey as a viscous barrier to bacteria and infection."  

Here are two abstracts that might interest you...If not, join me tomorrow for more information on using honey in our bath and body products! 

The anti-bacterial property and preservative nature of honey has been studied by evaluating the role of hydrogen peroxide in these properties, against bacterial strains isolated and identified from pasteurized milk samples. The antibacterial property of honey examined by agar incorporation assay and turbidometry, indicated a concentration dependent inhibition of bacterial growth in all catalase negative strains in comparison with catalase positive strains, highlighting a probable role of hydrogen peroxide. Samples of commercial milk stored at 40C in presence of honey were shown to inhibit opportunistic bacterial growth better compared to samples stored without honey. Due to the bactericidal property of hydrogen peroxide and its preservative nature, honey which is chiefly a combination of various sugars and hydrogen peroxide, can be used a preservative of milk samples.
Citation: Krushna, N., Kowsalya, A., Radha, S., & Narayanan, R. (2007). Honey as a natural preservative of milk. Indian Journal Of Experimental Biology, 45(5), 459-464.

To study the antimicrobial activity of honey, 60 samples of various botanical origin were evaluated for their antimicrobial activities against 16 clinical pathogens and their respective reference strains. The microbiological quality of honeys and the antibiotic susceptibility of the various isolates were also examined. The bioassay applied for determining the antimicrobial effect employs the well-agar diffusion method and the estimation of minimum active dilution which produces a 1mm diameter inhibition zone. All honey samples, despite their origin (coniferous, citrus, thyme or polyfloral), showed antibacterial activity against the pathogenic and their respective reference strains at variable levels. Coniferous and thyme honeys showed the highest activity with an average minimum dilution of 17.4 and 19.2% (w/v) followed by citrus and polyfloral honeys with 20.8 and 23.8% respectively. Clinical isolates of Staphylococcus aureus subsp. aureus, Escherichia coli, Salmonella enterica subsp. Enterica, Streptococcus pyogenes, Bacillus cereus and Bacillus subtilis were proven to be up to 60% more resistant than their equal reference strains thus emphasizing the variability in the antibacterial effect of honey and the need for further research.
C. Voidarou, (., A. Alexopoulos, (., S. Plessas, (., A. Karapanou, (., I. Mantzourani, (., E. Stavropoulou, (., & ... E. Bezirtzoglou (b, e. (n.d). Clinical Microbiology: Antibacterial activity of different honeys against pathogenic bacteria. Anaerobe, doi:10.1016/j.anaerobe.2011.03.012


Briny Bar Soap said...

Way cool. Thanks for the research that went into this. What're you going to school for?

Susan Barclay-Nichols said...

Fun! I've decided I want to be a polymath, so I've gone back to school to work on science and math. I'm really enjoying it! I have a degree in English and Canadian studies (I wanted to be a teacher when I was younger, but they weren't hiring due to the recession), but I want to round that out with some formal classes in math. It's been so interesting!

Hun said...

why is honey good when it is acidic?

Anonymous said...

highly informative! thanks

Tonje Richards said...

Could i use honey at 1-2% in combination with 1% citric acid and oils that are high in antioxidants to slow down the process of rancidity?
I only want my cream to last about 2-3 months out of the fridge.

Kind Regards,

Susan Barclay-Nichols said...

Hi Tonje. As I mention in the post, honey won't work to help something else remain bacteria free once it is diluted. Citric acid is an anti-oxidant, not a preservative, and you aren't really worried about rancidity in a few months with most of our oils. What you will need is a preservative to keep the lotion from going moldy, and neither honey nor citric acid are preservatives. Without one, your lotion has a life span of maybe a few days out of the fridge and a few days in the fridge. If you want to learn more, check out the preservatives section of the blog.

Omoge said...

Hi Susan , does a banana and sugar scrub contain enough water in the banana for mold to build? Will vitamin E preserve it for say a month?

Susan Barclay-Nichols said...

Hi Omoge. Vitamin E isn't a preservative, so it will not offer any protection from microbial contamination. It is an anti-oxidant, so it will retard the rancidity of your oils. Are you using real banana? If so, it has a shelf life of about a day. You cannot use real fruit in bath & body products that you hope to have last more than a day or two. Are you using banana powder? If so, you still need a very good preservative.

Anonymous said...

Hi Susan, what preservative do you recommend for homemade lotions? ect.

Susan Barclay-Nichols said...

Hi Anonymous! My policy is that comment without names will be deleted. Could you please edit it with your name somewhere in the post?

I encourage you to visit the preservatives section of the blog to see all the different options. I like liquid Germall plus.

Julia said...

Hi Susan! Thanks for the info. I have some questions about your bullet points.

"-Honey doesn't do well at higher temperatures and breaks down. If it breaks down, it's not going to be an effective preservative."

What if honey is added as the product is cooling down? Shouldn't that protect its efficacy?

"-Honey doesn't do well when diluted, and our water based products have quite a lot of water in them. (See the second abstract below)."

What about in an anhydrous product?

"-Honey will be in a less acidic product than it would normally be found. Our products tend to be in the 5.5 range. Although the neutralization of the honey's acidic pH is a good thing for releasing hydrogen peroxide, those enzymes are destroyed when exposed to heat and light, two things our products see regularly."

If the honey is mixed in during the cool down phase, and the product is stored carefully in UV resistant packaging, wouldn't that make a difference in the enzyme stability?

"-You would have to use so much that it would be the main ingredient in the product, and it would feel very very sticky."
If the only permitted preservative is honey, of course.

My question is, do you think in some preparations (added after cool down to an anhydrous or low available water formulation, stored in UV protected packaging) honey could yet be an effective partial preservative (piggybacked with another for full product protection)?

Vidyut said...

Forget honey preserving something else, while mead/honey wine exists on the planet, it is fairly clear proof that it won't even preserve itself on being diluted. I think a big part of honey's anti-microbial properties are because it is like a really thick sugar syrup that is too concentrated for anything to survive (In India, there are several sweet preserves made of fruits in sugar/jaggery syrup - notably mangoes and amla). Microbes get dehydrated and die.

However, honey may preserve something immersed in it when there is no water (much like sugar syrup). Fruits are difficult to preserve, yet last a year or more in syrup. As Susan pointed out, it will be sticky and the main ingredient. Only thing I muse about is what happens if the water phase of a product is only honey and the rest of the product doesn't need preserving. Worth experimenting and testing.

Susan has explained in reply to another comment that it won't work, but I didn't understand why it won't work.

Susan Barclay-Nichols said...

Hi Vidyut! I think it's explained in this post why it won't work. (There are quite a few reasons. One has to do with water activity. I think you posed a question in that post?)

Fruit isn't difficult to preserve. We do it all the time in jams through the use of lots of sugar. Again, we're back to water activity. Although, I guess it depends on your definition of "preserve"...

If you want to make a product that has a water phase only of water and want to use it, that would be interesting. I have no idea what will happen, but perhaps you could come back here and report your back your results. I think you'd have to get it challenge tested, which could cost some money, as a lot of contamination isn't obvious to the naked eye, but it's worth the cost to find out what's going on!

Can't wait to see your results!

flybysandy said...

Hi Susan!
If I would make a mask with honey (maybe around 80% of the formulation), carrier oils and some fruit powders (e.g. Camu camu, hibiscus, amla, guava fruit powder, raspberry. ......) or with some green powders (Chlorella, spirulina, matcha, moringa powder.......) do I need a preservative here? (There are no hydrous products like hydrosols in the mask.) There are many brands out there, which offer honey masks with manuka or hawaiian honey, oils and powders and co2 extracts and have no preservative in the mask. Is this ok? Can I make such a mask with honey, oils and powders without a preservative? Thank you so much for your answer. I am really wondering about this.
Kind Regards Sandra

Susan Barclay-Nichols said...

Hi Sandy. If you are keeping it more than a day yes, you need a lot of very powerful broad specrtrum preservative like Phenonip or Germaben II. I wouldn't suggest you actually make something that would be kept for more than a day, to be honest. Honey is a hydrous product. It contains water. It can only preserve itself. When you start adding all kinds of botanical things into the product, honey can't preserve those things.

I would never use a product without a preservative that was more than a few days old. I have a feeling that if we looked at those other products, we'd see an ingredient list that had a few things missing or you'd see a product that has had a recall or two in the past.

So the short answer is that no, you can't make a mask like this without a very good, strong preservative used at the maximum rate.

Love Great Products said...

Hi Susan,

I bought your ebook - Formulating Facial Products, and I just love it.
I have made myself a facial wash I have been using for the past 2 weeks. I used an organic castile liquid soap, Sunflower oil, Oil based extracts, essential oil and Honey @ 1%. I have added no water to this formulation.
I would like my product to last for at least 6 months. Do I need a preservative? Thank you in advance for your help

Susan Barclay-Nichols said...

Hi Love Great Products. Thank you for your kind words!
What's the pH of your final product?

Love Great Products said...

Hi Susan,

I posted an answer but I think it was lost somehow. But anyway, to answer your question as to the ph of my product is that I have not tested it. But I am thinking that the castile liquid soap I used is from a long time reputable company, and I would safely assume that it would be 7 to 10 on the scale. I know the oils I have added would change that some. I have been using the product and have experienced no harsh or drying effects.
After reading the blog on honey, I became concerned about the bacteria that might be forming. I was originally thinking that the castile soap would cancel out the need for a preservative and the honey would preserve itself. Does that make sense? lol. But now I just don't know. Thank you for a great and informative blog.

macharia njoroge said...

hi.can i use pure honey to preserve pure peanut butter considering it doesnt have any water?

Margaret said...

There is a lot of research showing honey's anti-microbial properties, which is why it is used to heal wounds. Check out the research done on Manuka honey. In science there are no absolutes, only theories and blanket statements such as "honey is not a preservative", should not be made.

Susan Barclay-Nichols said...

There are absolutes when it comes to preserving our products, and honey is not an adequate preservative for our products. A simple test can be done by making a water containing product that has no preservative. Then test it by putting samples of that product on a slide. If it shows signs of contamination, then honey didn't preserve it. I'd be happy to demonstrate this to you when I get my incubator up and running in a week or so.

In science, there are loads of absolutes, so to say that is wildly inaccurate. I could offer you a few examples. Pigs cannot sprout winds and fly. A human cannot live without a head. Light travels faster than sound on earth. To say there are only theories and blanket statements is just plain wrong as I've just demonstrated.

Having wound healing properties doesn't mean something is anti-microbial. It means it could speed up epthialization. And being an anti-microbial in one application wouldn't mean it was suitable in another. Bleach is an anti-microbial, but would you pour it in your eyes for an infection?

I've provided quite a few links to studies for you to read in that post. Perhaps you could provide a few to back up your statements? And please don't tell me to "do your research". I did, and I presented it to you. Please do me the same courtesy.