Wood Toxicity, Those Colors And Scent Are There For A Reason

Wood is made of the structural wood parts, cellulose and lignin, and what are known as secondary compounds. Secondary compounds are things that do not directly contribute to the tree being a tree, but rather serve a defensive purpose. Other organisms are always attacking trees. Fungus is trying to eat the tree, insects are boring into the tree looking for food and shelter (termites, carpenter ants), and animals are interested in the leaves and bark (beavers). Even bacteria is trying invade.

In response to these threats, trees developed chemical defenses. Hundreds, probably thousands of chemicals are produced by trees and are contained within the wood in order to stop or slow attack. These are secondary compounds also known as extractives. Extractives tend to be dark in color, and have a strong odor. The beautiful dark color of walnut is from extractives. The scent of cedar is from extractives. Many people are aware that cedar and juniper have traditionally been used in closets and to build drawers for clothing to keep insects away. This is an example of people using the natural anti-insects properties of a type of wood. However, just because people may find a wood sent pleasant does not mean that it is safe. Cedar, continuing the example, is notorious for causing various allergic reactions in humans. Like most chemicals, some people will be more sensitive to certain extractives, and some people will have a greater tolerance. Wood extractives are known be sensitizers in people. That is to say that the more someone is exposed to that extractive, the more sensitive they will be to it, sometimes leading to severe allergies, or even anaphylaxis.

Generally, woods to avoid are those with strong smells and or dark colors. Because of the environment where they grow, tropical hardwoods tend to have much higher amounts of extractives. Teak for example, a tropical hardwood, is well known for being very rot resistant, so much so that it has traditionally been used for boats and outdoor furniture. Though beautiful and durable, maybe we shouldn't be exposing ourselves to the same chemicals that are protecting the wood from bugs and fungus.

Lighter colored, lighter smelling hardwoods tend to have less extractives, and are generally much likely to cause allergies or sensitivities. In North America, this generally means Oak, Maple, Cherry and Ash.