Top 5 WORST Reptile Substrates

Finding the right type of substrate, or bedding, for your reptile can be very difficult. Whether you are working with a tropical gecko or a desert lizard, it’s important to know what to look for. It has to be safe, free of dust, non-toxic, non-irritating, absorbent, and not likely to be eaten – or at least be passed through the digestive system if it is.

Some substrates that are good for one environment type are not necessarily good for another. Similarly, some bedding is good for one type, but dangerous for another. You need to know your reptile species!

When it comes to choosing a bedding, use common sense. Any brand of pet litter that advertises clumping or scoopable is going to be a problem – this includes corn cobs, clay litter, and any kitty litter, which often contains clumping agents like bentonite and silica. Things that clump will stick to tongues and get into food; once swallowed, they can wreak havoc on the intestines. Sharp particles can also get into the mouth or cloaca and cause irritation and infection. Skin irritation can also occur – although scales look tough, reptiles actually can have rather delicate skin. Pet litters are often very dusty and can cause respiratory issues.

Don’t use sharp rocks, such as un-sanded, rough lava rock, as decoration, and avoid stones and gravel altogether for bedding, as they don’t cushion falls for climbing reptiles and are not good for burrowing. You can use them for a drainage layer, but they can be heavy so be cognizant when putting together a naturalistic enclosure. Larger, smoother stones are best for decor.

There are many options when it comes to reptile enclosures. So while there isn’t always a definitive BEST substrate, there are some contenders for the WORST. Especially ones that are specifically marketed to reptile keepers despite known concerns voiced by hobbyists and vets.

#5 Bark Chips

Fine grade orchid bark or cypress mulch can be fine for some species, but avoid chunks of hard bark or coco husk that are small enough to swallow. Animals are not able to break this down and it can stick in the gut, absorb moisture and swell, requiring surgery to remove.


Besides this danger, it’s not a great diggable substrate for burrowers and it does not hold heat very well.

Orchid bark is made from fir trees and is often sold in bags as “reptile bark” using a variety of brand names. It is low in dust and holds humidity very well, but this leads to problems of bacteria and mold growth, plus it’s a great place for mites to hide. Similarly, cypress mulch is an alternative that holds humidity well.

If you do use orchid bark or cypress mulch, make sure it is either too big to fit in your reptile’s mouth or is a fine, potting-soil type product. Mixed with coco fiber (the wiry “hair” on coconuts) or other small particulate substrates and covered with leaf litter, this is a great substrate for naturalistic terrariums. The danger lies in the size of the bark.

Bark chips could be an acceptable substrate for some reptiles, such as snakes that are tong-fed or placed in a separate enclosure to feed.

Avoid housing your lizards on bark chips, as they are very likely to ingest substrate as part of their food-finding routine of tongue-flicking and tasting. Wet foods such as greens can be dragged through substrate where chips can stick to the food item and swallowed. Some reptiles show interest in inedible items and will eat them despite not being viable foods.

#4 Silica Sand

These densely packed fine grains do not conduct heat evenly and can causes mild to extreme irritation of eyes, nasal passages and between scales. Further, long term exposure to the dust can cause silicosis, a disease of the lungs that develops after repeated exposure to silica dust. Most commercial sand products are made from ground quartz, which is silica in its natural form.


There are relatively few reptiles that live predominantly in sand; notable exceptions are shovel-nose snakes and sandfish skinks. Most desert-dwellers live in rocky outcrops or sun-baked clay with only a few patches of sand in their environment. These reptiles typically prefer burrows as a retreat to escape the heat of the day and the cold of the nights. Sand will not hold a burrow, requires moisture to keep down the dust, and does not retain heat. Sand-only enclosures should be avoided for most reptiles, even desert species.

However, sand can be an ingredient in terrarium substrate mixes, because when mixed with soil or cocofiber and moistened, the dust is under control and sand can add texture that is more pleasing for digging and holding a burrow.

Playsand is typically crushed quartz and should be washed because it contains dust. These dust particles (silica) are technically non-toxic if ingested, but can cause eye and lung irritation when it comes in contact with these organs. Severe cases include corneal scratches and silicosis, bronchitis and lung cancer. There are sands made without quartz so there is no silica dust to worry about. You can wash sand by getting a bucket, filling it halfway with sand and running a garden hose to float away the lighter dust particles. Stir gently and don’t use too much pressure or you will wash out the sand grains along with the dust. Mix with other substrates in ratios appropriate to your terrarium type: more sand for desert and less for tropical.

#3 Walnut Shells

Sustainable, attractive, inexpensive, low dust, absorbent. Ground walnut shells may seem like a good bedding choice, but in practice it has been found very problematic for a variety of lizards, especially Uromastyx and bearded dragons. These can very easily stick to food items or wind up in the animal’s mouth when going after prey.

Walnut detail

During the milling process, the particles are left jagged and sharp. Just pinch a grain between your fingers and apply pressure. Delicate eyes are at risk, and these ground shells can scratch corneas and otherwise irritate the eyes. They also pack a punch internally! When swallowed, they can not only cause impaction, but the pieces of shell can lacerate the stomach. Sounds very painful!

A similar ground product is corn cob bedding. It might not be as sharp, but there is possibility of swelling if eaten, not to mention harboring mold, bacteria, and smells.

#2 Calcium Sand

Calcium sand is probably the worst recommended and promoted reptile bedding sold by well-meaning pet store employees.


Reptile “calci sand” is not safe because it is too much of a good thing. It’s made from calcium carbonate – basically crushed antacid tablets. It would be fine if administered in small amounts on top of food as a calcium supplement, but over time, frequent ingestion will reduce stomach acid. This stomach acid is necessary to digest food and the supplement itself; once stomach acid is neutralized, the calcium carbonate will cause impaction. Constipation is a side effect in humans of taking antacid tablets, so this means that the mineral will likely never pass on its own, causing dehydration which further compounds the problem. The reason not all animals have an issue with it is some are less likely to eat it than others. It’s a very avoidable risk.

Calcium sand is also very dusty, and with any dusty product can irritate the eyes, nose, trachea and lungs.

#1 Ceder shavings

Cedar shavings have been used as animal bedding because they are soft, absorb moisture, control odors and repel fleas and other pets. Pine shavings, too, have similar properties. The potential health risks of these wood products, however, outweigh their benefits.

Western redcedar bolts

Some pet owners are already aware of the dangers posed by cedar shavings for small animals like rodents and rabbits. The cutting & processing the wood of Pacific redcedar Thuja plicata is linked to asthma, rhinitis, dermatitis, mucous membrane irritation, and central nervous system effects. There are few reliable animal studies; humans are the “guinea pigs” in these studies. There is much anecdotal evidence that cedar is flat out bad bedding for some critters.

The scent of pine and cedar that we humans find pleasant are a result of volatile oils that can cause damage to skin and respiratory systems. These shavings give off aromatic hydrocarbons known as phenols as well as acids that cause harmful reactions. In an enclosed space, an animal cannot escape the fumes from cedar wood shavings, and plicatic acid can actually destroy cells that line the lungs and trachea. Fleas and moths hate the stuff. Microorganisms hate the stuff. Humans with asthma hate the stuff, after chronic exposure. Please avoid cedar bedding!

Possible alternatives are aspen shavings, but this can also be dusty – it varies by the brand – and doesn’t hold humidity. It molds if too much moisture is present. Aspen can also be ingested while feeding, so only use it if it won’t stick to food; use tongs or feed in a separate tub.

Substrate Tips

Any indigestible particulate substrate, such as soil, cocofiber, sand, etc. can cause impaction if eaten in excess. When using a packaged bedding for horses or small animals, make sure you sift it and remove sharp pieces. Hemp bedding has been known to kill tortoises, so this is likely not a good choice, although some brands may be more finely processed and softer than others.

If you want to go with a more natural looking bedding instead of paper towel or other tank liner, follow these important steps:

  • House babies/juveniles on paper towel or tiles
  • Maintain adequate heating, with temperature ranges to allow thermo-regulation
  • Provide proper hydration through water bowls, spraying and humid hides
  • Ensure proper nutrition & supplementation
  • Keep food items off substrate using large plates or tiles or in elevated platforms
  • Provide furnishings that stimulate natural behaviors – climbing, basking, jumping, etc.
  • Monitor health for parasites and disease
  • Avoid stress, such as over-handling or bullying from cagemates

Geophagy, the eating of dirt, soil or clay, has been identified in nearly 300 animal species, including reptiles. It’s a sub-type of pica, the eating of non-food items. Eating substrate habitually can be the result of health issues or as an aberrant behavior due to captivity or a lacking environment.

A well-hydrated reptile can more easily pass swallowed substrate. Signs are obvious constipation, straining to poop, and dehydration as the material absorbs water in the gut. A vet trip is necessary, but extra hydration (moist foods and fruit) can help. Do not treat with home remedies like mineral oil as this can make medical treatment more difficult. Surgery may or not be required, depending on your vet’s diagnosis.

For most desert lizards, you can use ceramic tiles or stone slate tiles for a more natural look. This has the benefit of retaining heat and keeping claws filed down. You can use some washed playsand as a type of grout to hold the tiles in place, but be sure food will not be dragged through it and cause accidental swallowing. Dried clay like Excavator provides a safer burrowing substrate.

For jungle species, a mix of potting soil and peat moss or coir (coconut fiber) can be used with a top dressing of leaves or loose sphagnum moss. Be aware your geckos will likely lay eggs in this type of substrate, so a natural terrarium setup might not work for breeders.

Always research your bedding thoroughly! What is good for some won’t be right for all. Iguanas, tortoises, geckos, bearded dragons and snakes all have their own needs in terms of humidity and irritant sensitivity. Some are more likely to eat their bedding, out of curiosity or by accident. There are many reputable forums online that can help guide you. Every keeper has personal preferences, but you should get a wide variety of opinions before you decide. Every substrate has its own set of risks, and a bare floor is unfriendly to reptiles. You’ll need to decide what is appropriate for you and your pet.


The Dangers of Softwood Shavings, George Flentke.

High rat pup mortality attributed to the use of cedar-wood
shavings as bedding. Carol A. Burkhart & James L. Robinson. Laboratory Animals, 1978

Use of Cedar as a Substrate for Reptiles and Other Pets, Melissa Kaplan, 1994. Revised January 2014.

The toxicity of constituents of cedar and pine woods to pulmonary epithelium. GH Ayars, LC Altman, CE Frazier, EY Chi, The Journal of Allergy and Clinical Immunology, 1989.

Reptile Substrates, Melissa Kaplan, 1994, Revised January 2014.

Understanding Vivarium Substrates, Tortoise Trust.

Impaction & Constipation, Bearded Dragon Lady.–constipation.html

High Fungal Spore Load in Corncob Bedding Associated with Fungal-Induced Rhinitis in Two Rats. MA Royals, DM Getzy, S VandeWoude, Contemporary Topics in Laboratory Animal Science, 1999.

Hemp Beddding and Substrates for Tortoises – Danger Warning, A. C. Highfield, Tortoise Trust.

Calcium Sand Substrates – Dangers. Richard Brooks, HerpCenter.

QUIKRETE® Playsand Material Safety Data Sheet (MSDS), The QUIKRETE® Companies, Revised December 2011.

What is Silicosis? WiseGEEK.

Deer Fern Farms Uromastyx Care Page, Doug Dix.

Solving Problems of Reptile Eyes and Ears, Paul M. Gibbons, Michigan Veterinary Conference 2014.

Assessing Reptile Welfare Using Behavioural Criteria, Clifford Warwick, Phillip Arena, Samantha Lindley, Mike Jessop and Catrina Steedman. In Practice, March 2013

Why on earth?: Evaluating hypotheses about the physiological functions of human geophagy. SL Young, PW Sherman, JB Lucks, GH Pelto. The Quarterly Review of Biology, June 2011.

4 thoughts on “Top 5 WORST Reptile Substrates

  1. have just read about everything to put on the floor of my vivarium, I own spiny tails and have just thrown the calcium sand in bin and am at logger heads of what flooring to put down. please advise. thank you

  2. Hi! I’ve had a Greek tort for 5.5 years. Unfortunately he REFUSES to eat tort food, no matter what. I’ve tried very many methods, but no way would one work. He eats lettuce and only lettuce; which I know is not good on the long run. Any suggestions/help/advice would be highly appreciated.

    • Try chopping food finely into the lettuce and include a variety of grains. Depending on the ingredients, commercial tortoise food is only a supplement, most of their food should be dried grasses, fresh greens or safe weeds, veggies like squash, and some fruits like raspberries. Some tortoises may also take edible flowers like squash blossoms. Some tortoise pellets are mostly dry hays which can be a staple of the diet but limit the amount of pellets made from soy or corn as grains and legumes should be a small portion of the diet. Good luck!

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