Wood handle - toxic species and harmful factors in the manufacture and operation

Unfortunately, the average life expectancy of a knife maker is significantly shorter than that of people who do not have this hobby. It is a fact. And the point here lies not so much in unhealthy technological processes of metalworking and complex steel ligatures, but, oddly enough, in elementary non-compliance with safety standards in the manufacture of handles from various (exotic and, it would seem, the most common) wood species. This article summarizes the results of several scientific works by foreign researchers on various wood toxicity factors that arise both at the stages of its processing and at the stages of further operation of products.
To begin with, a few historical facts to assess the severity of the problem. Fatalities have been reported when using food utensils made from yew wood. Bows were made from the same yew in medieval England, and almost all archers suffered from an allergic rash on their hands. Attempts to play musical wind instruments made from cocobolo wood, as a rule, ended in death for musicians. Houses built from western thuja logs caused acute respiratory diseases in residents. An attempt to cut down the swamp cypress led to chronic diseases of the eyes and nasopharynx in lumberjacks. And there is a huge amount of such evidence, of varying degrees of tragedy.
Below is a table of one of the studies on the toxicity of various types of wood and the hazards that arise when working with them.

#	Type of wood	Body reaction	Impact localization	Impact	Source of toxicity	Photo
1	Arizona Cypress, Bald Cypress, Red Cypress, Yellow Cypress, Southern Cypress (Bald Cypress)	Increased sensitivity	Airways	Weak	Dust
2	Balsam Fir	Increased sensitivity	Eyes, skin	Weak	Leaves, bark
3	Beech	Hypersensitivity/ Cancer of the nasopharynx	Eyes, skin, respiratory tract	Medium	Leaves, bark, dust
4	Birch	Increased sensitivity	Airways	Medium	Dust, wood
5	Robinia, false locust, black locust (Black Locust, False Acacia)	Irritation/ Nausea	Eyes, skin	Strong	Leaves, bark
6	Ebony, African blackwood	Increased sensitivity	Eyes, skin	Medium	Dust, wood
7	Boxwood	Increased sensitivity	Eyes, skin	Medium	Dust, wood
8	Cashew, Anacard, Akazhu, Kazhu (Cashew)	Increased sensitivity	Eyes, skin	Weak	Dust, wood
9	Cocobolo	Increased sensitivity/irritation	Eyes,skin, respiratory tract	Strong	Dust, wood
10	African Piptadenia, Dahoma, Dahoma	Annoyance	Eyes, skin	Medium	Dust, wood
11	Ebony	Increased sensitivity, irritation	Eyes, skin	Medium	Dust, wood
12	Elm (Elm)	Annoyance	Eyes, skin	Weak	Dust
13	Astronium ash-leaved, Goncalo (goncalo) alves, Tiger tree (Goncalo Alves)	Increased sensitivity	Eyes, skin	Medium	Dust, wood
14	Greenheart of Suriname	Increased sensitivity	Eyes, skin	Strong	Dust, wood
15	Red Canadian Cedar, Hemlock	Nasopharyngeal cancer	Airways	No data	Dust
16	Chlorophora high, Iroko	Sensitivity/lung disease/irritation	Eyes, skin, respiratory tract	Strong	Dust, wood
17	Large-leaved luminescence, Mahogany	Sensitivity/lung disease	Respiratory tract, skin	Weak	Dust
18	Mansonia high	Increased sensitivity/irritation	Eyes, skin	Strong	Dust, wood
19	Maple (Maple), including those infected with fungus, marbled (Spalted)	Sensitivity/lung disease	Respiratory tract	Strong	Dust
20	Mimosa	Nausea	No data	No data	Leaves, bark
21	Notofagus Cunningama, Myrtle	Increased sensitivity	Airways	Medium	Leaves, bark, dust
35	Sassafras	Increased sensitivity	Airways	Weak	Dust
36	Sequoia	Annoyance	Airways	Weak	Dust
37	Piratinera Guiana, Snakewood	Annoyance	Airways	Medium	Dust, wood
38	Spruce	Increased sensitivity	Airways	Weak	Dust, wood
39	Walnut	Increased sensitivity	Eyes, skin	Medium	Dust, wood
40	Milletia Lawrence, Wenge	Increased sensitivity	Eyes, skin, respiratory tract	Weak	Dust, wood
41	Willow	Increased sensitivity	Airways	Weak	Leaves, bark, dust, wood
42	Giant thuja, folded (Western Red Cedar)	Increased sensitivity	Airways	Strong	Leaves, bark, dust
43	Teak	Sensitivity/lung disease	Eyes, skin, respiratory tract	Medium	Dust
44	Yew	Annoyance	Eyes, skin	Medium	Dust
45	Zebrawood Astronium	Increased sensitivity	Eyes, skin	Medium	Dust, wood

It must be said that the data given in this table allow only an approximate assessment of the risk factors when working with a particular wood. Since very general names of trees are often given, which may include entire classes of species, in general, with different factors and degrees of toxicity (with a more detailed table of the correspondence of harmful factors to certain tree species, indicating the family and the exact botanical name, you can read  here ).

An example of such a generalization is the red tree - the name that a very large number of different breeds (by the way, almost all of them cause a burning sensation in the nose and eyes, which feels like tear gas, so you need to work with them extremely carefully, in compliance with all safety measures). Or boxwood, which grows in different parts of the world and, depending on the region of origin, has completely different properties, even wood looks radically different. This partly explains some of the differences between previous results and data from other studies, such as those shown in the following table:

Another factor that should be taken into account when evaluating the results of such studies is the individual sensitivity of a person to toxic components. According to statistics, up to 5% of people are hypersensitive to one or more allergens contained in wood. You can determine in advance the reaction of your body to the wood of a particular species and avoid contact with irritant wood or take exceptional safety measures when working with it. Each person has their own immune system and symptoms may not appear immediately, but with the accumulation of a critical value of allergens in the body. An allergic reaction, in the form of a rash on the skin, most often appears on the thinnest and most sensitive areas (usually between the fingers). The rash is possible in the form of redness, urticaria, small bubbles. The reaction of the respiratory tract to the primary irritant is a cough. In more severe cases - difficulty and pain in breathing, heaviness in the chest, suffocation.
Dangers can come not only from exotic woods and not only from the chemical components contained in wood. A fairly common cause of allergic reactions are fungal cultures living on it. The best known of these is Cryptostroma corticale. The product of the vital activity of this fungal culture is the spall of wood in the form of the so-called marble rot, and often the wood is specially infected to obtain this effect. Unfortunately, this flexible, living under the bark of deciduous trees, mainly maple and birch, is a strong allergen and causes the disease of “maple bast harvesters” known for a long time.
By the way, such seemingly harmless wood as birch - similar in symptoms to the impact on the human body with the African or Indochinese paduk. Inhaling the dust of this wood in large quantities can cause one of several systemic reactions: runny nose, nausea, headache, kidney or heart failure, hallucinations. Also, birch, and even more willow, contains a huge amount of salicylic acid (aspirin) in wood. People with hypersensitivity to this drug should be careful with these tree species. I would also like to separately note two species of trees, with especially toxic properties, having a centuries-old reputation as poisoners and requiring special care in handling. These are yew and oleander. They contain large quantities of the so-called cardiac glycosides - potent drugs, very dangerous even in small doses.

According to the results of various studies, nasopharyngeal cancer in people who regularly inhale wood dust occurs 5 to 20 times more often. And although the reasons are not exactly established, but as a rule, this fact is associated with a high content of tannins (tannins) in wood dust (the highest content of tannins is present in the wood of chestnut, oak, arborvitae, sequoia and hemlock). In general, with all the variety of negatives when working with wood, the most important harmful factor, which many times overrides all the others in terms of impact and consequences for the human body, is wood dust. When working with wood, you need to proceed from the fact that wood dust is a priori harmful and when processing wooden blanks, you need to work only in a mask and with a hood.
For most people who are not related to woodworking, it would be a reasonable question - how safe is the handle of a knife or other everyday tool made from exotic woods in operation. First, as already noted, the main harmful factor is wood dust, which is absent in this case. Secondly, real harm from tactile contact can only occur in extremely poisonous trees, for example, in the yew and oleander mentioned above. It may not be worth buying a knife with a handle from these breeds. Thirdly, modern impregnations used in the manufacture of knife handles and other tools penetrate the wood so deeply and reliably protect its surface that it is hardly worth worrying about any toxins that can break through such a protective layer. Wood Compatibility Optionsdifferent breeds with the most popular impregnations used for handles are shown in the table below ("+" is good; "-"  is not suitable; "+/- " suitable in some cases):

Some of the results presented in this table can be called quite controversial. For example, the author of this study recommended beeswax only for oak wood, and then not in all cases, but he ignored drying oil and various additives, such as rosin, in general, and this can be argued with. But for the most part, everything else can be somehow agreed and taken as a basis if there are no own developments for specific cases.

In conclusion, I would like to note that if you want to have a knife with a wooden handle or even want to make it yourself, an alternative would be material such as preserved wood. During stabilization, the wooden blank is impregnated through and through, forming a polymer monolith that reliably binds wood components and minimizes harmful factors. In addition, stabilized wood has excellent mechanical properties during processing - it does not have differences in density along the body of the workpiece (which allows for more accurate drilling and sawing), it is polished without clogging the skin, it is polished into a mirror. At the same time, the appearance and tactile sensations remain inherent in ordinary wood.

Observe safety rules! Treat wood in a well ventilated area and work in respirator.