This article is courtesy of Michael Sims and Erica Skadsen:
With the proliferation of wood jewelry manufacturers on the market, Organic LLC and Esoteric Body have been working in partnership to study various chemical compositions of individual hardwoods and their effects on the human body, in hopes of providing information that could assist you in safer wood jewelry selection. Over the past few years we have undertaken extensive research on wearable hardwoods and have found numerous woods to be unsuitable. These potentially harmful species have documented medical reactions that may result in contact dermatitis or more extreme effects. We are not referring to respiratory reactions to sawdust, but rather to dermatological reactions due to direct skin contact with the wood.
We caution against believing a product is safe just because someone offers it to the public. Many suppliers pick their woods because they are attractive, but often they know little about the wood itself. It is alarming that body jewelry manufacturers and distributors often do not take the responsibility to thoroughly research their products before they offer them for sale to the public; few even learn the scientific names of the species they use. This message is not meant to provoke other than to encourage study and discussion. Instead, we intend this to be a helpful guide which can be used to navigate the vast jewelry market and to make a more informed decision by knowing what the hazards are. As the popularity of wood body jewelry continues to increase, we felt that it has become a necessity to supply the community with information that we have gathered. We hope it will prevent hardwood enthusiasts from having an unnecessarily negative experience with these materials. There are many wearable hardwoods out there that are quite safe, but unfortunately there are also many species that pose risks or are unsafe for use against the skin. We encourage buyers and producers alike to undertake your own research and to find your own answers.
Despite repeated requests to do so, there are several reasons we will not publish a comprehensive list of woods that are safe and woods that are not safe for use as body jewelry materials: • There are many thousands of wood species, and researching the chemical structure and dermatological response patterns of each is beyond the scope of this paper, and indeed, would take a lifetime of dedicated research. • The potential to react with woods from either list remains highly variable from person to person, amongst other factors, and thus there can be no universally valid safe or unsafe list. • Any attempt at doing so oversimplifies the complex nature of the issue, and would give a false impression of homogeneity to an extremely diverse range of materials.
Health Concerns and Risks
While much of the research available to woodworkers is a good starting point, it was not designed as a guide to the wearability of woods. The problem is that most documentation specifically addresses wood dust and not actual skin contact with wood. Wood dust produces an extremely large amount of surface area, which has a much greater potential to produce problematic reactions during the manufacturing process than exposure to the amount of surface area that is in contact with the skin in the case of completed wood products.
Interestingly, most published research seems to base reports on only a few case studies, many of which go back up to 100 years; some of studies list only common names and not specific species of wood, and results are not obtained by clinical studies with large sample groups. However, these isolated cases should not be entirely dismissed; they are relevant in showing patterns of cross-sensitivities, and many have been accompanied by positive patch tests from extracts of the offending compounds.
The structure of wood is primarily composed of the biological polymers cellulose, hemicellulose, and lignin, along with some inorganic minerals. In addition, secondary metabolites are produced in wood which build up in the center of the tree, becoming its heartwood. These substances are called extractives. Besides providing characteristic color and scent to wood, they can provide chemicals beneficial to humans, but may also cause health problems (such as allergic reactions), as they are essentially toxic biocides made to defend the tree against decay or predatory attacks. "Some of these act as food reserves for latent growth periods, some as hardening agents, and others protect against mechanical injuries or attack by bacteria, fungi, insects and larger animals (Dietrichs 1958). Some are metabolic by-products or end-products of no apparent use to the tree." 1
Exposure to the chemistry of any substance has the potential to cause biological effects. Acute exposure is described as "a single, brief contact" of varying intensity, while the cumulative effects of "repeated or prolonged contact" of chronic exposure may not occur until a greater length of time has passed. Most problems from skin exposure to wood will be localized, rather than systemic - involving the whole body when chemicals are absorbed into the blood stream, which is more of a risk when dealing with the respiratory effects of wood dust. Permanence and reversibility of the effects depend on a variety of factors, including degree and site of exposure, type of chemical, and the reaction history and level of sensitivity in the person exposed.
"The main effect is irritation." An irritant is a substance that causes an excessive response, soreness, or inflammation, which can entail heat, swelling, redness, or pain. ..."This can be caused by skin contact with the wood, its dust, its bark, its sap, or even lichens growing on the bark. Irritation can, in some species of wood, lead to nettle rashes or irritant dermatitis. These effects tend to appear on the forearm, backs of the hands, the face (particularly eyelids), neck, scalp, and the genitals. On average, they take 15 days to develop." 2 While acute effects from primary irritants can occur immediately upon exposure, latency periods can range from a few hours to several months. "Symptoms usually only persist as long as the affected skin site remains in contact with the source of irritation... Symptoms subside when contact with the irritant is removed." 2
"Sensitization dermatitis is more problematic and is usually caused by skin exposure to fine wood dust of certain species." 2 Sensitization is "an allergic reaction to a substance which is usually irreversible" resulting in hypersensitivity and susceptibility to being overly responsive. Dermatitis is inflammation of the skin. ..."This is also referred to as allergic contact dermatitis and results in similar skin effects to those produced by skin irritants. Once sensitized, the body sets up an allergic reaction, and the skin may react severely if subsequently exposed to very small amounts of the wood dust." 2 "Cross-sensitization can occur between two different species if both contain structurally related sensitizers." 3
"An allergy is the adverse health effects which result from the stimulation of specific immune responses."4 "Allergic contact dermatitis is a form of delayed-type hypersensitivity reaction which is dependent upon cell-mediated immune function and the activity of T lymphocytes."4 The most frequent form of allergic reaction is to small molecular weight materials such as chemicals and proteins. These reactions are better known as contact hypersensitivity, skin sensitization, and allergic contact dermatitis. Delayed-type reactions (as opposed to those with more immediate effects from primary irriatants) occur in two stages:
• "Phase I (Induction): Initial contact... may result in [the allergen] penetrating the stratified squamous epithelial cells of the skin and binding to large dendritic (branched) white blood cells in the epidermis called Langerhans cells. The Langerhans cell (with [the allergen] on its membrane) migrates to a nearby lymph node where special white blood cells, called effector T-cells, are programmed to recognize [the allergen]. There are literally millions of effector T-cells roaming throughout the blood and lymphatic system, each with special receptor molecules on their membranes for a particular allergenic chemical. ... T-cells patrol our circulatory system looking for invading cells and viruses." 5
• "Phase II (Elicitation): If [contact occurs with the offending allergen] during a subsequent encounter... an effector T-cell may encounter it bound to a Langerhans cell and attach to it by a complicated and specific recognition system. The effector T-cell then produces more clones of itself and releases special proteins called lymphokines which attract a legion of different white blood cells, including macrophages and cytotoxic ("killer") T-cells. The new army of white blood cells releases cytokines or proteins which destroy everything in the vicinity... including other skin cells, thus producing a blistering rash... Milder effects range from redness (vasodilation) and itching (nerve injury) to small blisters (vesicles and bullae)." 5
Stronger effects can result in anaphylaxis, which can occur in response to any allergen; while anaphylaxis occurs infrequently, it is life-threatening and can occur at any time. While the percentage of people that may react to or become sensitive to the compounds found in wood is small, it will always remain a possibility. Risks include prior history of any type of allergic reaction, though these effects can also occur in those without previous reactions.
The culprit behind most of these allergies is a group of naturally occurring chemicals called quinones. They represent just a few of the numerous extractives residing in the heartwood and other tissues of various species, which are produced as defensive agents against fungal, microbial, and other predator attacks (including woodworkers and jewelry collectors). Quinones are often used to make dyes; for example, lawsone, the active ingredient in the henna plants Lawsonia inermis and L. alba, is the red-orange colored pigment 2-hydroxy-1,4-naphthaquinone, a molecule known as hennotannic acid. Though they also have potential cosmetic (such as their use in skin-lightening formulas) and medicinal uses (various quinones have been studied for their antibacterial, anti-tumor, and cancer fighting abilities) in non-allergic humans, quinones play a major role in allergic contact dermatitis caused by plants.
The primary "allergens are benzoquinones or naphthoquinones but also compounds, such as catechols and other phenolic or flavonoid compounds, which are bioconverted [metabolized] into ortho-quinones or para-quinones." 3 These derivatives can covalently bond to skin proteins. Since they are not recognized by the immune system, they are attacked. Catechol is a main constituent of urushiol, which is the allergen in poison ivy. Certain types of coumarins can also be sensitizers when they form ortho-quinones via enzymatic oxidation within the skin.
It is possible that once sensitized to one of these quinones that cross reactions to similar quinones and/or compounds can develop. In other words, a reaction to a quinone component of one wood can make someone more susceptible to future reactions to other wood allergens.
Some of the other compounds that have been known to cause harmful responses include: alkaloids and glycosides ("systemic effects, pharmacological rather than allergic"), dalbergiones (severe skin irritants), long-chain phenols ("the strongest skin sensitizers," especially "the catechols" in urushiol "of the poison ivy family" Anacardiaceae), furocoumarins and coumarins (sweet-smelling photosensitizing and anticoagulant phenolic compounds; may be carcinogenic and partly responsible for skin reactions but has yet to be proven), saponins (effective through broken skin only), stilbenes (which "occur in allergenic woods, but only chlorophorin... and coniferyl benzoate... are known to sensitize"), terpenes ("including delta-3-carene from turpentine, sesquiterpene lactones... and other sensitizing" compounds which can be within lichens and "liverworts found on bark, and euphorbol and other complex terpenes of uncertain toxicity found in the latex of Euphorbiaceae"), aldehydes, and ketones. 1
Not all substances have equal potential to yield dermatological problems. Some, such as the dalbergiones and catechols, are much more effective than others. Even the different types of quinones can cause varying results.
Included below is a list of some of the more popular woods that may be unsuitable to wear due to these risks. There are other hardwoods that are notorious for causing dangerous reactions - which may include surprisingly strong reactions such as cardiac and nervous system effects, cancer, and genotoxicity - such as: afromosia (Periocopsis elata), Australian blackwood (Acacia melanoxylon), greenheart (Chlorocardium rodiei), mansonia (Mansonia altissima), sassafras (Sassafras albidum), and satinwood (Chloroxylon swietenia), as well as various softwoods such as: cedar (Thuja spp.), hemlock (Tsuga spp.), pine (Pinus spp.), and yew (Taxus spp.); however, these are not discussed here because we have fortunately not seen their attempted use in body jewelry.
List of popular woods to avoid, to minimize the risk of adverse effects.
Most of this information is taken from:
Botanical Dermatology: Plants and Plant Products Injurious to the Skin.6
Bibliographies listing the works by the authors cited in parenthesis can be found in the BoDD Database. 6
We will continue to expand this list as we further our research. Note that we are listing research specific to the heartwood of trees; toxins can be found in a species that is not found in its wood. For example, cyanide is found in apple seeds, but the fruit is edible, even though it is in close proximity to this toxin. "Toxic activity is specific to a wood species. Knowing the exact species is important in establishing what the potential toxic effects may be. Individual wood species... are very easily confused. For example, 'rosewood' may be used for up to 30 different species; and an individual species may have up to ten different trade names (Hausen 1981). An additional difficulty is that trees vary within a species. One specimen may contain low levels of its toxic agent and the next contain much higher levels. So experience may not be a reliable guide." 2
Dalbergia spp (Rosewoods): "The discovery of sensitizing quinones in other woods such as teak...led Schulz and Dietrichs (1962) to look for similar substances in Dalbergia nigra and Dalbergia retusa. They found three quinones which they called Dalbergia quinones A, B and C, and demonstrated by patch tests on patients that these were the sensitizers, the strongest being R-3,4-dimethoxydalbergione... They have now been found in most other Dalbergia spp." 6
Dalbergia cearensis (Kingwood, de Violette, Violet Wood, Violetta): contains a dalbergione, "described as a very severe skin irritant, often leading to persistent ulceration." 6
Dalbergia cochinchinensis (Laos Rosewood, Thai Rosewood, Cochin Rosewood): "contain R-4-methoxydalbergione and other quinones." 6
Dalbergia congestiflora (Mexican Kingwood): contains a dalbergione. 6
Dalbergia cultrate (Burmese Rosewood): contains a dalbergione. 6
Dalbergia decipularis and Dalbergia frutescens (Tulipwood): contains a dalbergione. 6
Dalbergia latifolia (East Indian Rosewood, Sonokoling, Sono Wood): contain R-4-methoxydalbergione and other quinones. 6
Dalbergia maritime (Madagascar Rosewood, Bois de Rose): contains a dalbergione. 6
Dalbergia melanoxylon (African Blackwood): "contains several quinones including S-4'-hydroxy-4-methoxydalbergione... and S-4-methoxydalbergione." 6
Dalbergia nigra (Brazilian Rosewood): "contains R-4-methoxydalbergione and other quinones (Schulz and Dietrichs 1962)." 6 This species is also endangered, and is listed under CITES Appendix I as threatened with extinction.
Dalbergia retusa (Cocobolo): "contains S-4'-hydroxy-4-methoxydalbergione, R-4-methoxydalbergione and other quinones and phenols" 6 such as obtusaquinone. 7
Dalbergia stevensonii (Honduran Rosewood, Nagaed Wood, Palissandre Honduras): contains a dalbergione. 6
Acer saccharum (Sugar Maple): "This species has been found to contain 2,6-dimethoxy-1,4-benzoquinone which is a known contact allergen." 6,7
Betula spp (Birch): various parts of the tree contain salicylates such as methyl salicylate 6, which can cause dermatitis; cross-sensitivities could occur in those with aspirin allergies. Birch also listed as sensitizer. 8
Cinnamomum camphora (Camphorwood): "The wood contains camphor and borneol." "Following cases of serious toxicity and even death in children, products containing more than trace quantities of camphor have now largely been withdrawn from the market (Reynolds 1996)." "Can cause dermatitis and shortness of breath" and camphor causes mild heart stimulant activity. Topically applied, it can penetrate the skin. 6
Cordia dodecandra (Ziricote, Zericote) and Cordia elaeagnoides (Bocote, Becote): Cross reactions are possible with these species if sensitivity to R-3,4-dimethoxydalbergione (in pao ferro and Dalbergia species), obtusaquinone (in cocobolo), and macassar quinone (in Macassar ebony) has developed. "Some members of this family [Ehretiaceae] appear to have the capacity to sensitize on contact. The cordiachromes, which are terpenoid benzoquinones, appear to be the compounds responsible." 6
Diospyros celebica (Macassar Ebony): contains "macassar II, a ß-naphthol derivative" that "may become oxidised in vivo to macassar quinone. This compound has been shown to have sensitizing properties... Cross-sensitivity to other naphthoquinones has been demonstrated". Cross-sensitivity has also occurred "to R-3,4-dimethoxydalbergione (found in pao ferro), obtusaquinone (found in cocobolo), and macassar quinone (found in Macassar ebony)."
"The yellow naphthoquinone pigment, plumbagin (methyl juglone) occurs in a colourless combined form and is liberated from root tissue by acid treatment. (Harborne 1966)... Plumbagin is also found in some species of the families Droseraceae, Ebenaceae, and Euphorbiaceae (Thomson 1971).... Plumbagin has an irritating odor and causes sneezing; it stains the skin to a purple color and has a vesicant action." 6
We have only found evidence that quinones have been proven to occur in the wood of the ebony species Diospyros celebica (widely distributed), and D. melanoxylon 7 (not normally commercially available).
Guibourtia tessmannii (Bubinga): contains 2.6-dimethoxybenzoquinone 7, and can cause dermatitis. 2, 8
Machaerium scleroxylon (Pau Ferro, Pao Ferro): "Dalbergiones were found to be the allergenic components of the wood" 6, including R-3,4-dimethoxydalbergione 6,7, a strong sensitizer and irritant.
Milletia laurentii (Wenge): can give dermatitis and induce "central nervous system effects." 2 Wenge contains 2.6-dimethoxybenzoquinone. 7
Peltogyne densiflora (Purpleheart): "Dalbergiones have been isolated from the wood (De Sousa et al 1967)." 6
Piratinera guianensis and P. paraense syn. Brosimum guianense and B. paraense (Snakewood and Satine Bloodwood, Cardinalwood): Quinones were discovered in the wood (Hausen 1970). 6
Salix spp (Willow): contains salicin, a phenolic glucoside, and is a precursor of aspirin; also has saligenin, a known contact allergen. 6 Willow is also listed as a sensitizer. 8
Tectona grandis (Teak): The "dermatic compounds" (sensitizers) lapachol (aka tecomin, a quinone), desoxylapachol (a naphthoquinone), and lapachonole (aka lapachonone) were found in Tectona wood.
Lapachol has been called "a known elicitor of contact dermatitis" and a "sensitizing agent."
"Deoxylapachol and lapachenole...are potent contact allergens."
"Local races of teak and even individual trees vary greatly in desoxylapachol content."
"Lapachenole has been shown to be both irritant and sensitizing by Sandermann & Barghoorn (1955)." 6
Tetraclinis articulata (Thuya Burl) - a type of softwood: "The heartwood of this species is known to contain several dermatologically active compounds including thymoquinone, carvacrol, and ß- and γ-thujaplicins." 6
Other woods that we are investigating further at this time include:
Pterocarpus soyauxii (Padauk): can cause irritation of the skin, allergic contact dermatitis 9, and sensitization. Cross-sensitivity has occured with use of ziricote, bocote, pao ferro, cocobolo, and Macassar ebony when sensitivity has been developed to related quinones. 6
We are still in the process of determining the exact allergenic compound(s) within padauk wood.
Quercus rubra (Red Oak) contains 2.6-dimethoxybenzoquinone. 7
Swietenia macrophylla (American Mahogany, Bigleaf Mahogany) contains 2.6-dimethoxybenzoquinone, 7; trees from the Neotropics are listed under CITES Appendix II as protected species.
Dymondwood(R) is a manufactured plywood product consisting of laminated layers of hardwood (likely birch) veneer which have been colored with mono-azo acid dyes and then compressed under intense heat and pressure with phenol formaldehyde resin into a dense, durable, highly polished material. Interestingly, Bakelite, a type of early thermoset synthetic resin, is a polymer of phenol with formaldehyde. Many Dymondwood(R) varieties go by cute trade names, but it can usually be identified by its appearance as a brightly colored wood product with consistently spaced stripes in contrasting colors not normally appearing in untreated wood. Besides cropping up periodically in the body piercing world as earplugs, it is common to find it utilized in other products such as pipes and bracelets.
Phenol, also known as carbolic acid or hydroxybenzene, is toxic and corrosive. The dangers posed by formaldehyde, including its role as a carcinogen, are also substantial. According to the MSDS for Dymondwood(R), "Phenol and formaldehyde may be released in small quantities from product under normal conditions." "Some people may develop dermatitis from repeated and prolonged exposure to unfinished product." "Laboratory data indicates that certain acid dyes may be mutagenic in animals." 10 The azo dyes (azo is a chemical compound containing one pair nitrogen atoms with a double bond between them) may release aromatic amines if the azo linkages are broken down via enzymes, or possibly via heat and photochemical reactions, though intact azo dyes are unlikely to be absorbed by the skin. However, these aromatic amines have been linked to serious long-term health effects, including links to cancer in humans, so the possibility of their presence is of grave concern. Incidentally, azo dyes are sometimes used as pigments in tattoo ink.
Unfortunately, dyes are also commonly used overseas to make lighter woods appear as black ebony. These commonly include aniline or PPD. Aniline is a blood toxin that is easily absorbed through the skin, which may cause allergic skin reactions and irritation, contact dermatitis, sensitization, is a possible carcinogen, and is considered very toxic to terrestrial and aquatic life. 11 PPD (para-Phenylenediamine, aka para-Aminoaniline, 1,4-Benzenediamine, or 1,4-Diaminobenzene), is an aromatic amine dye, used to color hair, and used extensively in SouthEast Asia to apply temporary black "henna" "tattoos." It is easily absorbed through the skin, and has been called a significant allergen and toxin. It can cause allergic contact dermatitis, cross-sensitization to other chemicals, rash, blisters, chemical burns, and permanent skin changes such as scarring, renal failure, anaphylactic shock, or even death.
There is a huge range of chemicals used to treat wood, ranging from pesticides, fungicides, preservatives, and fumigation meant to kill insects and microorganisms, most often before lumber is offered for sale, to finishes such as oils, waxes, lacquers, and varnishes, as well as adhesives used to join inlay materials or splice wood together for a striped appearance. Each has a chemical makeup that should be thoroughly investigated before their utilization in wood products intended to be in contact with skin.
After lengthy research we have put together this guide to help educate shop owners, end users, and hopefully some of the manufacturers producing potentially dangerous products. While reactions will not occur in all individuals, they can range from irritating to life-threatening, and the possibility that these effects may be elicited, along with the risk of becoming cross-sensitized to other materials, should be taken very seriously. It is up to you to be informed about what you are buying and putting into contact with the human body. Wood jewelry is one of the most comfortable and grounding materials we have available to us, and can be both an aesthetically pleasing and safe material if potential hazards are identified, understood, and avoided.
1. Woods, Brian and Calnan, C.D. "Toxic Woods." British Journal of Dermatology, Supplement 13, 1976.
2. HSE Information Sheet: Toxic Woods, Woodworking Sheet No. 30, reprinted December 2003.
3. Lepoittevin JP, Benezra C. "Allergic contact dermatitis caused by naturally occurring quinones." Pharmacy World & Science/Pharmaceutisch Weekblad Scientific Edition, Volume 13(3), 21 June 1991: 119-22. Review.
4. Kimber, Ian and Maurer, Thomas. Toxicology of Contact Hypersensitivity. CRC Press, 1996.
5. Epstein, W. L. "Allergic Contact Dermatitis." Current Perspectives in Immunodermatology, Churchill Livingstone Press, 1984: 253-263.
As referenced in: Armstrong, W.P. and Epstein, W.L. "Poison Oak: More Than Just Scratching The Surface." HerbalGram: The Journal of the American Botanical Council, Volume 34, 1995: 36-42.
6. Mitchell, John and Rook, Arthur. Botanical Dermatology: Plants and Plant Products Injurious to the Skin. Vancouver: Greengrass Ltd., 1979. A summary and database is also available online.
7. Hausen BM. "Sensitizing capacity of naturally occurring quinones. V. 2,6-Dimethoxy-p-benzoquinone: occurrence and significance as a contact allergen." Contact Dermatitis, Volume 4, August 1978: 204-213.
Also see the related articles: Schulz, KH, Garbe, I, Hausen BM, and Simatupang, MH.
"The sensitizing capacity of naturally occurring quinones." I and II:
"I. Naphthoquinones and related compounds." Archives of Dermatological Research, Volume 258, 1977: 41-52.
"II. Benzoquinones." Archives of Dermatological Research, Volume 264, Number 3, January 1979: 275-286.
8. Arno, Jon, Dr. Dimitriadis, Eugene, Flynn, Jim, and Tandy, Roy. "4 specialists' insights on toxicity of selected woody species across the planet," World of Wood. March 2000: 4-12.
Republished as: "Insights on Wood Toxicity," in A Guide to Useful Woods of the World, edited by Flynn Jr., James H., Holder, Charles D., and Stamm, Susan. Madison, WI: Forest Products Society (FPS), and International Wood Collectors Society (IWCS), 2001. Also available online through this link.
9. Kiec-Swierczynska, Marta, Krecisz, Beata, Swierczynska-Machura, Dominika, Palczynski, Cezary. "Occupational allergic contact dermatitis caused by padauk wood (Pterocarpus soyauxii Taub.)." Contact Dermatitis, Volume 50, Number 6, 2004: 384-385.
10. MSDS Dymondwood(R).
11. MSDS Aniline.
- Hausen BM. Woods Injurious to Human Health: A manual. Berlin: Walter de Gruyter & Co., 1981.
- Woodcock, Robert, R.N., B.S.N., C.E.N. "Toxic Woods." Art Hazard News, Volume 13, Number 5, 1990. New York: Center for Safety in the Arts.
Apparently the source of the chart popularly attributed to American Woodturner. June 1990. Also available online; it has been quoted, modified, and reposted on numerous websites.
- CITES (Convention on International Trade in Endangered Species)
- MSDS p-Phenylenediamine.
IF YOU THINK YOU ARE HAVING A REACTION TO WOOD, REMOVE THE ITEM AND SEEK MEDICAL ATTENTION IMMEDIATELY
The first edition of this guide was co-written by Erica Skadsen and Michael Sims in 2005; the second edition was published in May 2006; the third edition was published in June 2007.