The upswing in demand for natural products is generally good news for human and environmental health, but with this enthusiasm come some misunderstandings. When inquiring about ingredients or the appropriate use of a potential product I’m sometimes shocked by the answers I get from the product manufacturer representatives. For example, I once heard something like “All of our ingredients are completely natural, so it is safe for all species”.

Let’s pick apart this statement. First of all, just because something is natural doesn’t mean it is safe. Second, some natural substances are toxic to some species but not others. There are many other considerations as well, most notably dose. Let’s look at these three variables more closely:

Substance – There are countless natural substances that are quite toxic to people. Consider lead and its devastating effects, particularly on children. Lead is natural, but really really bad when ingested by people. Botulinum toxin, produced by the bacterium Clostridium difficile, is the cause of the deadly disease botulism. It is the most toxic protein known — yet it is completely natural.

Species - Plants can be toxic to some species but not to others, or affect species to various degrees. For example, most of us know that humans can eat large amounts of chocolate without (acute) health consequences, but dogs really should not do this. Lilies are toxic to cats but not to people. Black cherry leaves can be toxic to all animals, but ruminants (e.g., goats, cattle, sheep, deer) are at higher risk than monogastric [one stomach] animals (e.g., humans, dogs, cats, pigs, horses) and birds because of their gut anatomy.

Dose - For most substances, it is the dose that makes the poison. In fact, many of our common medications are quite useful when taken in an appropriate dose, but harmful if too much is given. Consider acetaminophen, the active ingredient in Tylenol. Given in the correct dose it is quite effective for the relief of fever and pain, but too much can result in liver damage. Most pharmaceuticals follow this pattern, including those derived from plants. The heart medication digoxin is a derivative of digitoxin, the active ingredient from the foxglove plant. A little bit helps the heart; a lot will stop it.

Other factors – Consider the age, size, sex, and health status of the person or animal using the substance. From a plant perspective consider the part of the plant used, condition and maturity of the plant, as well as its growing conditions. Finally, consider the exposure time and the way a product is used (e.g., ingested, inhaled, applied to the skin).

Natural is not always safe. What is good for one may not be good for another. More is not always better. Our natural world holds tremendous potential, but we need to invest in careful study to demonstrate the effects — both the ones we’re after and the ones we’re not.