EUROPEAN  TISSUE  REPAIR  SOCIETY

NOT ALL HONEYS ARE THE SAME FOR WOUND HEALING
P. C. Molan PhD, Associate Professor of Biochemistry and Director of the Honey Research Unit
University of Waikato, Hamilton, New Zealand

There is rapidly increasing interest in the use of honey as a wound dressing because of its properties of rapid clearance of infection (including infection with antibiotic-resistant bacteria), rapid debridement of wounds, rapid suppression of inflammation, minimisation of scarring and stimulation of angiogenesis and the growth of granulation tissue and epthelium. (Further information on this, and a bibliography, can be obtained at: http://honey.bio.waikato.ac.nz) This is a 'rediscovery' by the medical profession of an ancient method of treating wounds, a method that has continued into present-day traditional medicine around the world. But unlike the ancient physicians and today's practitioners of traditional medicine, medical professionals are not aware that all honeys are not equal in their therapeutic properties. Nor are many researchers who carry out investigations of the effectiveness of honey against various species of bacteria. All treat honey as a 'generic medicine' and give no consideration to the large variance that occurs in therapeutic components in natural products.

Aristotle (c.350 BC) wrote that 'Spring honey is sweeter, whiter, and in every way better than the autumn honey' and 'White honey does not come from thyme pure and simple; it is good as a salve for sore eyes and wounds'. Dioscorides (First century AD) wrote that 'the best honey is from Attica, the best of that from Mount Hymettus, next best is from the Cyclad Islands and from Sicily. Spring honey is best, then Summer honey' and that 'honey that is sharp, of a fragrant smell, is pale yellow and thixotropic is good for all rotten and hollow ulcers'. There is a similar awareness in present-day folk medicine: in Sardinia strawberry-tree honey, and in Dubai honey from the Jirdin valley of Yemen, are highly valued for their therapeutic properties; in India, lotus honey is said to be a panacea for eye diseases; in New Zealand it was the long-standing reputation of Manuka honey for its antiseptic properties that prompted the laboratory investigations that led to it being found that it had an unusual antibacterial component. In laboratory studies where multiple honeys have been tested against the same strain of bacteria, up to a hundred-fold difference in antibacterial potency has been found. Large variations in the content of antioxidants in honeys (which also are probably of importance in wound healing) have also been found.

Dr Peter Molan

There is also a large variation in the physical quality of honey that is on sale. Although comb honey is used in some traditional wound treatment, when it is crushed on to the wound the honey then has introduced into it as contaminants the particulate matter adhering to the outside of the comb, as well as the pieces of wax in which the honey was contained. Honey that is purchased extracted from the comb has similarly been contaminated by the crushing or the cutting off of the cell caps of the comb during processing, this often being done in facilities that would not meet minimum hygiene standards for processing other foods, let alone medical products. The honey is then strained to remove visible particles, but the mesh used for straining is usually not fine enough to remove particles of contaminants that potentially could give rise to granu-lomas if they get embedded in healing wounds. Nor will any form of filtration feasible with honey remove bacterial spores. Although honey inside the cells of the comb is sterile, and its antibacterial properties will kill any vegetative bacteria introduced into it during and after extraction from the comb, any bacterial spores introduced will not be killed, and viable spores of clostridia are sometimes found in honey. To remove such risks, honey processed especially for wound care is available: this is extracted and processed in facilities with hygiene standards as for the manufacture of wound dressings, using 'state-of-the-art' machinery for filtering out small particles whilst exposing honey to minimal heating to protect heat-labile therapeutic components, and then sterilised by gamma-irradiation.
Honey sold especially for wound care also has standardised antibacterial activity. Although all honey has antibacterial activity due to its high osmolarity, it soon fails to suppress growth of bacteria on a wound as it becomes progressively diluted by exudate. Whereas a honey with no antibacterial beyond the osmolarity would cease to stop the growth of Staphylococcus aureus once diluted four-fold or more, honey sold especially for wound care would still be inhibitory if diluted more than sixty-fold. Another consideration is that because a concentration gradient is set up as antibacterial activity diffuses from the surface down into the tissues of the wound bed, the higher the activity on the surface, the deeper down an inhibitory level of activity will be maintained. A clinical trial will be necessary for the importance of the additional antibacterial activity in honey to be unequivocally proven, but anecdotal reports indicate that it makes a difference to the rate of healing.

Similarly, a clinical trial will be necessary for it to be known for certain which type of antibacterial activity in honey gives the best therapeutic effect. All honey, to varying degrees, has an antibacterial activity due to hydrogen peroxide formed in a 'slow-release' manner by the enzyme glucose oxidase present in honey. Some honeys have additional antibacterial activity due to phytochemicals from the nectar of particular species of plants. In Manuka honey, and honey from some other Leptospermum species, there can be a high level of activity due to such a component, this having a broad spectrum of antimicrobial activity. (This activity, the 'Unique Manuka Factor', is rated as the 'UMF' number of honeys on sale.) Although laboratory testing against a range of species of bacteria has shown that for most species a honey with a median level of activity due to hydrogen peroxide and a Manuka honey with a median level of the phytochemical antibacterial component are equally as potent, there are some reasons why in a clinical setting the Manuka honey could be expected to be more effective. Because of the presence of catalase in serum and tissues, some of the hydrogen peroxide produced in honey will be decomposed, but the phytochemical antibacterial component will maintain its activity. The glucose oxidase enzyme that produces hydrogen peroxide in honey becomes active only when honey is diluted, but the 'unique Manuka factor' is active in full strength honey, thus giving a more potent antibacterial action diffusing into the depth of infected tissues. Glucose oxidase has low activity at low pH, so will not give honey its full antibacterial activity until the acidity of honey has been neutralised by dilution with wound exudate, whereas the 'unique Manuka factor' is fully active at low pH. Also, the glucose oxidase in honey could possibly be digested by protease activity in wound exudate. It is for these reasons, and the excellent anecdotal reports coming from clinical usage of Manuka honey, that the honey on sale at present especially for wound care is honey with a standardised level of 'unique Manuka factor' activity.

Dr P. C. Molan
Honey Research Unit
Department of Biological Sciences
University of Waikato, Private Bag 3105
Hamilton, New Zealand
Tel: +64 7 838 4325
Fax: +64 7 838 4324
E-mail: pmolan@waikato.ac.nz

Dr. Peter Molan with his team at the Honey Research Unit, Department
of Biological Sciences, University of Waikato, Hamilton, New Zealand.