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The Outdoor Factor? Natural healing from trauma in tortoises

Updated: Mar 26

A massive trauma and a wild Testudo hermanni found in a field in Greece. The tortoise was active, feeding, and had clearly sustained the injury several years previously.

We often get asked "What are these dry, white marks on my tortoise's shell?". The answer is that they are areas of dead bone caused by various trauma injuries to the shell. These include bangs and scrapes, burns, predator attacks, aggression from other tortoises or even ticks (which can attach to the softer new growth areas between the scutes). All of these damage the top layer of keratin, which is pretty thin as you can see from the example of the dead tortoise carapace.

In a living tortoise there are three layers: The outer keratin, an intermediate membrane rich in nerves and blood vessels, and finally the bony skeleton beneath. This too is living tissue. If the outer keratin is penetrated, infection can get into that intermediate layer and can also damage the bone to certain extent. This then dies off and dries out. This is what these white, dry 'chalky' pieces actually are.

A clear view of how once the outter keratin has been destroyed though trauma or infection the underlying bones of the carapace also dry out and die (to a certain depth).

Another example of a tortoise fully recovered from major trauma injury that would have ocurred at least 2 years previously. In this case the fracture of the carapace extends from top to bottom.

The truly remarkable thing about tortoises is that their natural healing processes include the ability to re-generate the keratin underneath the dead pieces of bone. These eventually wear off or fall away (it can take a very long time, sometimes years), revealing new keratin underneath. See our earlier notes on carapace regeneration following wildfires. They really are remarkable animals! It is also especially interesting to see how they recover from sometimes massive injuries in the wild without antibiotics ,or any other intervention. Some of our recent research suggests that exposure natural solar Infra-red-A and to high intensity visible light generally may play a significant role in this by reducing microbial infection and by stimulating the regeneration of new tissue.

A wild tortoise showing clearly how a new (dark) layer of keratin forms between the live bone beneath and the dead bone above... the old, white dead bone layer eventually wears off and falls away, leaving a fresh layer of protective keratin.

This is a somewhat speculative article. It is really just our thoughts on what might be going on, and is 'food for thought'. It does not purport to provide definitive answers. We have seen, over the years, many, many quite incredible recoveries in the wild from traumas that based upon our experience over a similar term with captive tortoises, we would not have expected survival - let alone such complete recoveries. For example, without triage, irrigation, disinfection and maintenance in a clean environment plus antibiotics, we would have anticipated serious, probably fatal, secondary infections in all of these cases. Yet, that appears not to have happened.

It was while reflecting back over a whole sequence of case records like these that prompted us to think about why. Is there something we do not understand happening here?

We began to encouter reports in the medical literature of how exposure to natural sunlight can potentially have measurable effects upon wound healing and the prevention of infection. As we began to dive deeper into this, it became clear that this possibility could not be dismissed as a cause of what we were observing. It is even more curious because it is generally accepted that exposure to air (as occurs in the wild) can actually hinder wound healing (wounds tend to heal best when moist) - though there is other evidence that in some circumstances, an open-to-air wound might be less suseptible to secondary infections by anaerobic bacteria. It is a complex area, and there are numerous variables, and a few contradictions as above. There appears to be few certainties. Two areas of special interest soon became clear, however: water-filtered (atmospheric) infrared-A and high intensity visible spectrum light.

Interestingly, specialist lamps that emit water-filtered infrared-A 'WiRa' are increasingly being used in both human medicine and veterinary medicine to accelerate wound healing, to reduce pain, reduce inflammation, increase oxygen in tissue and considerably reduce the dangers of secondary infection. It is very important to stress that this is not myth or mere theory - but reality supported by multiple rigorous studies in peer-reviewed medical and veterinary journals.

However, it is equally interesting to reflect upon the fact that in some ways here, we do seem to have an example of mythological 'wisdom' coinciding with something that we know now to be scientific fact. In ancient times solar deities were typically also associated with healing. This was so in Roman, Greek and Egyptian cultures as well as many others around the world. Coincidence? Regardless, it is a persistent cross-cultural trait that 'healing' has long been associated with the sun.

The pleasant, 'deep heat' warming effect of the sunlight actually arises from the filtering of the infra-red radiation of the sun by water vapour in the atmosphere of the earth. This filtering effect of water molecules in the atmosphere decreases the energy (by absorption) of those parts of the infrared spectrum (infrared-B and -C and the absorption bands of water within infrared-A), which would then cause, by reacting with water molecules in the surface layers of skin, an undesirable thermal load in that region. The latter, in fact, is exactly what occurs when reptiles are exposed to 'normal' heat lamps. The surface later of the skin heats up rapidly and their spectra has an intense drying and dehydrating effect not only upon water molecules in the skin and keratin, but ultimately in the animal's body as a whole. By contrast, atmospherically water-filtered infrared-A penetrates to deeper levels without 'dumping' large amounts of concentrated energy upon the surface, avoiding the intense dehydration effects, and making it both safer, more comfortable and more effective.

The beneficial effects of solar infra-red upon trauma injuries and wound healing are reported in medical journals as:

  • Acute pain reduction

  • Larger and faster reduction of the wound area

  • Higher tissue oxygen partial pressure (O2 diffusion)

  • Higher deep tissue temperatures

  • Lower wound infection rates

  • Accelerated granulation and epithelial regeneration

  • Reduced injury site exudation

The higher recorded tissue oxygen levels are important because wound healing is an energy consuming process, and energy production in tissue depends upon an adequate supply of oxygen. Therefore oxygen partial pressure and perfusion are crucial factors for improving the supply of energy and oxygen to tissue, and this has a direct effect upon the overall healing process.

It is not just this type of effect that is interesting here, however. Natural full sectrum sunlight has also been found to have highly effective antimicrobial properties. In one such experiment to find alternative methods of combatting aggressive, drug-resistant bacteria, irradiation by natural sunlight was found to inactivate almost 100% of all the target antimicrobial-resistant bacteria after just five hours of exposure. Curiously, another peer-reviewed study that examined the anti-microbial effects of sunlight found that even sunlight that had passed through a pane of window glass still remained quite effective against many classes of microrganism - which suggests that there is more involved than UV radiation, which is blocked by glass. This, the authors suggest, provides "evidence to the hypothesis that sunlight may be used to selectively limit the viabilities of microorganisms in buildings like hospitals". The majority of pathogens that cause airborne infections cannot tolerate sunlight, oxidants or the temperature extremes that occur outdoors. One paper concludes "Visible light at high intensity was found to kill bacteria while low-power light in the visible and near infrared region enhances bacterial proliferation". In this context we should note that almost all captive reptiles, when kept out-of-range and certainly indoors, are subject to massively lower light intensities than they receive in their natural habitats.

Could this be a factor in why we see so often captive animals succumb so readily to injuries and infections, even with veterinary intervention, while wild examples appear to be able to recover from similar injuries unaided?

Clearly not all do survive, but a significant number certainly do, even with injuries that those of us who have experience of similar injuries in captive animals find both surprising and impressive. We do not yet fully understand this, and we have far more questions than answers currently, but it seems to us that there is undoubtedly something unusual going on in these cases.

While the effects of visible light on cell metabolism (photobiomodulation) have been demonstrated in multiple papers, the fundamental mechanism of action is not comprehensively understood. It appears multiple pathways may be activated, with the specific effects being highly dependent on the wavelength and intensity of the light applied. From a broad survey of papers discussing this topic, it appears that light in the 'blue' spectrum (415nm) might be especially important in this respect (Lubert, et. al 2011), though other studies also identify cellular effects from the red spectrum.

This is - quite simply - something to consider and in our view certainly justifies a more thorough investigation.

Please note that we are in no way suggesting that injured tortoises are simply kept outside or denied qualified veterinary attention! We are merely suggesting that mechanisms may exist that play a role in the recoveries of tortoises IN THE NATURAL HABITAT that deserve further attention.


Azuma T, Hayashi T. Effects of natural sunlight on antimicrobial-resistant bacteria (AMRB) and antimicrobial-susceptible bacteria (AMSB) in wastewater and river water. Sci Total Environ. 2021 Apr 20;766:142568. doi: 10.1016/j.scitotenv.2020.142568. Epub 2020 Oct 1. PMID: 33066962.

Carreau, A., Hafny-Rahbi, B.E., Matejuk, A., Grillon, C. and Kieda, C. (2011), Why is the partial oxygen pressure of human tissues a crucial parameter? Small molecules and hypoxia. Journal of Cellular and Molecular Medicine, 15: 1239-1253.

Fahimipour, A., Hartmann, E., Siemens, A. et al. Daylight exposure modulates bacterial communities associated with household dust. Microbiome 6, 175 (2018).

Hartel M, Illing P, Mercer JB, Lademann J, Daeschlein G, Hoffmann G. Therapy of acute wounds with water-filtered infrared-A (wIRA). GMS Krankenhhyg Interdiszip. 2007 Dec 28;2(2):Doc53. PMID: 20204084; PMCID: PMC2831241.

R. Lubart, A. Lipovski, Y. Nitzan and H. Friedmann. A possible mechanism for the bactericidal effect of visible light. Laser Therapy. 2011; 20(1): 17–22.

H. Schumann, T. Calow, S. Weckesser, M.L. Müller, G. Hoffmann, Water‐filtered infrared A for the treatment of chronic venous stasis ulcers of the lower legs at home: a randomized controlled blinded study, British Journal of Dermatology, Volume 165, Issue 3, 1 September 2011, Pages 541–551.

Hoffmann G, Hartel M, Mercer JB. Heat for wounds - water-filtered infrared-A (wIRA) for wound healing - a review. Ger Med Sci. 2016 Jun 29;14:Doc08. doi: 10.3205/000235. PMID: 27408610; PMCID: PMC4928028.

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Text add images copyright (c) 2024 A. C. Highfield/Tortoise Trust.

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