Does Loose Substrate Cause Impaction in Bearded Dragons and Other Reptiles?

Does loose substrate cause impaction? It’s a question we see in reptile forums (particularly for bearded dragons and leopard geckos) every day! Impaction — also known as a blockage of the gastrointestinal tract — is often attributed to the use of loose substrates such as sand. Does this mean that loose substrate be avoided at all costs? Or is it necessary to achieving satisfactory welfare for captive reptiles?

The subject of impaction is shrouded in myth and misinformation. This confuses hobbyists and perpetuates husbandry practices that many would argue, including myself, are damaging to animal welfare by denying entire aspects of their behavioural repertoire.

Reptiles Need Loose Substrate

For now, let’s put aside the question of whether loose substrate really causes impaction. (Don’t worry — we’ll address that in a minute.) For now, I’d like to concentrate on the behavioural need for loose substrate. If we look at the Animal Welfare Act (2006), we will find the Five Animal Needs stated, one of which being “the need to be able to exhibit normal behaviour patterns”.

screenshot of the 5 Needs listed in the Animal Welfare Act

And as we have covered in another video, the requirements of the Animal Welfare Act are considered to be the bare minimum, only promoting up to satisfactory welfare.

Let’s look at two very popular reptile species in our hobby: the bearded dragon and the leopard gecko.

Care practices for both species are often shrouded in folklore husbandry beliefs, which aggressively assert that impaction is caused by the ingestion of loose substrate. Both also have a behavioural need to dig, which allows them access to different microclimates in their wild environment. Refusing to provide a loose substrate in a bearded dragon’s or leopard gecko’s captive environment restricts their ability to dig and satisfy this instinct. Therefore, according to the parameters set forth by the Animal Welfare Act, this type of setup fails to meet even the minimums of satisfactory welfare.

Furthermore, consider this: Many of the same people who keep bearded dragons/leopard geckos and routinely object to loose substrate also routinely use loose substrate in the form of lay boxes when they want to breed their animals. See how confusing this is? If loose substrate is believed to be so hazardous to the animals’ health, and routinely quoted as “not worth the risk,” then why is it suddenly okay to subject the animal to such a risky substrate when it needs to lay?

In response to this, some might say, “Well, the animal won’t be able to comfortably lay without access to loose substrate. We still believe it to be a unnecessary risk, but so is the risk of the animal becoming egg bound. So we provide it temporarily because it is needed in this special case.”

Well, that’s fine, but aren’t you simultaneously acknowledging the fact that loose substrate is needed for the animal to engage in natural behaviour? What about its behavioural need to dig outside of egg laying?

When you think about the issue from the perspective of animal welfare requirements, rather than hearsay, the argument against loose substrate really starts to unravel.

Does Loose Substrate Cause Impaction?

In a healthy reptile? No!

A healthy reptile — whether it be bearded dragon, leopard gecko, or other — will not get impacted as long their husbandry is correct. The correct temperatures, the correct amount of vitamin D, and adequate hydration are all needed for a healthy reptile. It is only when one or multiple aspects of husbandry are off that the animal becomes compromised and impaction becomes a possibility. A compromised animal can become impacted from paper towel, insect chitin, and other materials just as well as it can become impacted from loose substrate. Impaction is a symptom of an underlying issue, rather than the root cause. Removing loose substrate, therefore, only masks the real problem.

The mineral CaCO3 (calcium carbonate) composes more than 4% of the earth’s crust and is present planet-wide. It’s found in chalk and limestone (a common component in soil), as well as in biological material such as bones and shells. Not coincidentally, calcium carbonate is present as the main source of calcium for most reptile calcium supplements.

Zoo Med Repti Calcium powder supplement

Geophagy is a completely natural wild behaviour for many reptiles. The consumption of earth to supplement mineral needs has been observed in many species. Some also hypothesise that reptiles ingest substrate, like birds, to create gastroliths that assist in the mechanical digestion of food.

If an organism evolves to engage in purposeful geophagy, then the accidental ingestion of small amounts of substrate isn’t a feasible danger in a healthy animal. An evolved behaviour like this would not have persisted if it were so likely to cause impaction and subsequent death.

But isn’t the sand/soil in reptile enclosures much looser than in the wild?

One common argument against the use of loose substrate is that “the soil is hard and compact in the wild, so tile is actually very natural.” While I do admit that there are likely times that reptiles spend time on rocky, hard surfaces, for the most part this isn’t true.

Take bearded dragons for example (which this argument is commonly used for). Dr. Jonathon Howard once posted a video of the wild habitat of the central bearded dragon. In this video, he quite clearly viewers a very loose, sandy substrate.

After sending samples of the substrate to Southern Cross University for laboratory analysis, its composition was confirmed as the following:

  • 0.3% gravel
  • 95.9% fine sand (quartz, coloured by iron oxide)
  • 1.5% silt
  • 2.3% clay

If bearded dragons evolved to live on such a substrate, then they must have evolved the necessary adaptations for interacting with said substrate, whether it be digging or ingestion.

Also, if the animal evolved to spend most — if not all — of its life on such a soft substrate, what is the potential for long-term damage to the joints of an animal living its entire life on a solid, hard surface? What about the damage to the joints of overweight individuals (which many captive bearded dragons are), which are already under unusual stress? It is well known the long-term knee issues that joggers who consistently run on concrete get, and the many types of running shoes are designed to combat this exact issue. Think about how this may apply to bearded dragons, leopard geckos, and other reptiles kept on a hard substrate.

Alright Then, What DOES Cause Impaction in Reptiles?

If loose substrate doesn’t cause impaction, what is causing all of these cases of impaction that keepers and veterinarians are talking about?


One of the main causes is a fundamental misunderstanding of the hydration needs of “desert” species. Many impacted lizards are severely dehydrated lizards. These two conditions tend to go hand-in-hand. If the lizard is dehydrated, then lubrication of organs and the ability to pass particulates through the digestive tract can be reduced. In fact, even the ability to pass urates can be impaired by dehydration.

In bearded dragons, when urates are formed, they are transported to the distal colon for storage.

does loose substrate cause impaction? - a look at bearded dragon gastrointestinal anatomy

This is where the colon absorbs excess water from waste. This is also where the urate suspension transitions to water. In healthy bearded dragons, a semi-solid urate plug is discharged during defecation.

does loose substrate cause impaction? - a look at bearded dragon gastrointestinal anatomy

In a dehydrated dragon, the colon is also dehydrated, causing its walls to contract around the urate fluid. This strips out more water than usual, causing a solid mass to form and adhere to the colon mucosa. Less lubrication and a desiccated, hard urate make passing difficult. The same applies to substrate ingestion.

does loose substrate cause impaction? - a look at bearded dragon gastrointestinal anatomy

How do bearded dragons and other “desert” reptiles get so dehydrated?

To help answer this question, I got in contact with popular Australian veterinarian, Dr. Jonathon Howard (otherwise known as “BeardieVet”), and asked about the daily humidity in the central bearded dragon’s natural habitat. He informed me that:

  • humidity at dawn and dusk is 55-65%
  • by midday, it has dropped to 20-30%
  • at night, humidity can rise up to 75-80%

This report excludes microclimates where bearded dragons are known to hang out, such as the bases of bushes or burrows. These areas can certainly reach 80% humidity.

While I do acknowledge that I do not specify season or month where this data was recorded, it’s safe to say that the humidity in the central bearded dragon’s native habitat is not 10-15% like some keepers try to achieve, insisting that bearded dragon enclosures must be as dry as possible, or else the dragon will get a respiratory infection.

I believe this is one of the primary husbandry issues in captive bearded dragon care, regardless of impaction. Well-meaning keepers are dehydrating their animal and even refusing to provide a water bowl because they are under the false impression that “desert species don’t need water.” And yet, they insist on regularly bathing their dragons in the effort to keep it hydrated, despite the fact that bearded dragons are not semi-aquatic, nor do they regularly spend time near bodies of water.

My point here is this: ambient humidity in the wild reaches far higher percentages than many keepers believe. When the air is too dry even for these moisture-conserving, desert-adapted species, this leads to rampant dehydration and impaction.

Low Basking Temperatures

If the basking area temperatures are not high enough to allow a reptile to achieve its preferred body temperature (PBT), then their bodies don’t have enough energy to function properly. As one of the results, digestive functionality can be decreased, as well as slowing gastrointestinal peristalsis. Peristalsis is the rhythmic contractions of the intestines to move food along. When the gastrointestinal tract isn’t moving, things can get stuck.

Not Enough Vitamin D

In a study conducted in 2019 on humans, lower levels of 25-hydroxyvitamin D were linked to reduced colonic transit times and chronic functional constipation: “At multivariate analysis, vitamin D low levels remained a significant independent risk factor for the occurrence of intestinal motility disorder”.

 Yes, this is a human study, not a reptile study. However this problem applies to most — if not all — vertebrates. If UVB provision or vitamin D supplementation is insufficient to the point that the animal becomes 25-hydroxyvitamin D deficient, then intestinal motility becomes reduced and the likelihood of impaction rises.

Poor Diet

Another cause can be poor diet:

  • Not enough roughage to promote healthy defecation
  • Too much chitin from overfeeding of insects
  • Dehydrated feeder insects
  • Reduced organ movement due to obesity

Sufficient quantities of roughage are required to promote healthy defecation. Overfeeding combined with a lack of exercise leads to obesity, which in turn reduces organ movement. Overfeeding of insects specifically will result in an overabundance of chitin in the diet. Combine that with poor hydration of the feeder insects themselves, that too can contribute. That is why it is vital we highlight the importance of proper feeder insect nutrition and gut loading.

Symptoms of Impaction in Reptiles

If you are concerned that your reptile may have become impacted, the symptoms of impaction are as follows:

  • Lack of appetite
  • Struggling to defecate, or not defecating at all
  • Lethargic behaviour
  • Partial paralysis of the back legs

Treatment of colonic obstruction includes soaking the animal in shallow, lukewarm water for half an hour to 2 hours. This may encourage defecation, thus temporarily solving the problem.

Soaking in warm (not hot!) water for 30 minutes daily for 7 days may help with rehydration, and may stimulate more frequent defecation of softer faeces while the digestive tract heals.

This is the only time I would bathe a reptile — when there is a purpose for it. If your reptile has become impacted, it is essential to correct the husbandry errors that led to the animal becoming impacted in the first place.  Healthy terrestrial reptiles do not need routine soaking or bathing. It should be enough to provide sufficiently high humidity levels and a water bowl large enough for them to soak in as desired.

As always, veterinary advice should always be sought and any diagnosed underlying conditions treated, this not a substitute for veterinary care. And if you are concerned with the health of your animal, seek veterinary help immediately.    


To summarize:

Does loose substrate cause impaction in bearded dragons and other reptiles?

No — not when the reptile is healthy.

Can you provide adequate welfare to an animal without loose/natural substrate?

No — not when you consider the Five Needs of Animal Welfare.

The only situation in which the complete avoidance of natural substrate becomes advisable is when the animal is undergoing quarantine and needs its enclosure to be frequently disinfected, or in instances where the animal’s health is impaired.

bearded dragon quarantine enclosure
This bearded dragon is in a quarantine setup.

Other than that, a healthy reptile should absolutely be housed on a natural substrate that caters to its specific behaviours, therefore increasing its welfare in a captive environment. Bioactive substrate is also an option, but that is beyond the scope of this article.

If you have recently been challenged on your choice to use natural substrate, show them this article or its associated video. If you find yourself debating the same old argument over this topic, use this article. If you are passionate about the welfare of captive reptiles, share this article.

About the author:

Liam Sinclair author photoLiam Sinclair is a keen reptile owner that has worked as a zookeeper as well as in a specialist reptile shop in the UK. He is currently pursuing a degree in Animal Management, and he currently runs the YouTube channel, Reptiles and Research. His goal is to help people achieve higher welfare for their animals.


Animal Welfare Act, http://www.legislation.gov.uk/ § 9 (2006)

Grosett, C., Daniaux, L., Guzman, D. S., Weber, E. S., III, Zwingenberger, A., & Paul-Murphy, J. R. (2014, May). (PDF) Radiographic anatomy and barium sulfate contrast transit time of the gastrointestinal tract of bearded dragons (Pogona vitticeps). Retrieved from https://www.researchgate.net/publication/260306715_Radiographic_anatomy_and_barium_sulfate_contrast_transit_time_of_the_gastrointestinal_tract_of_bearded_dragons_Pogona_vitticeps

Howard, J. [BeardieVet]. (2019, March 11). Bearded Dragon Substrate [Video]. YouTube. https://www.youtube.com/watch?v=d1YJ8tXu3cI

Mitchell, M., & Diaz-Figueroa, O. (2005, April 07). Clinical Reptile Gastroenterology. Retrieved from https://www.sciencedirect.com/science/article/abs/pii/S1094919405000095?via=ihub

Wright, K. (2008). Two Common Disorders of Captive Bearded Dragons (Pogona vitticeps): Nutritional Secondary Hyperparathyroidism and Constipation. Journal of Exotic Pet Medicine, 17(4), 267–272. doi:10.1053/j.jepm.2008.07.004


  1. Any recommendations for what I should use instead? I personally hate using paper towels and wanted it to be temporary anyways