250 species in 10 genera are found in the northern hemisphere, south to Sumatra, Java, central America and the West Indies.
[Summary yet to be added]
50 species are found in north temperate regions and central America.
Species of this genus are commonly named fir or whitewood and, in Great Britain, European silver pine, etc. (Handbook of Softwoods 1957).
An extract of fir made by the method of Fregert and Rorsman (1963) was used to investigate 125 patients for dermatitis suspected to be caused by woods. Positive patch test reactions were observed in six males and two females. In these eight patients, a commercial extract of fir obtained from Hollister-Stier Laboratories, Spokane, Washington produced positive patch test reactions in two cases. Contact sensitivity to fir was considered significant in four of the males, three forest-workers and a farmer. The farmer bedded his cattle on fir shavings; when he changed his bedding to straw, his hand dermatitis cleared (Mitchell 1970).
At the Finsen Institute from 1935 to 1963, 12 cases of contact dermatitis from "fir" wood were observed (Hjorth 1965). Some firs cause woodcutter's eczema from lichens or liverworts (Frullania spp.) growing on the bark (Tenchio 1948).
Abies pectinata is listed as injurious by Hanslian and Kadlec (1966). Farmers who felled and sawed silver fir during the winter developed recurrent dermatitis of the hands and arms spreading to the face and neck at that season only. Patch tests to fir resin gave strong positive reactions (Ganzoni 1929). Siemens (1929) reported dermatitis from the foliage of silver fir; patch tests were not recorded.
This species has traditionally been used as a Christmas tree (see also Picea abies H.Karst. below). It is the source of Alsatian turpentine and Strassburg turpentine (Usher 1974).
This species is the source of Canada balsam, otherwise known as Canada turpentine (Terebintha Canadensis) or Balsam of Fir, a viscous yellow-green oleoresin. Applied to the skin, Canada balsam produces redness and slight irritation; and is frequently employed as a stimulant to indolent and erysipelatous ulcers; it likewise enters into the composition of several salves and irritating plasters (Felter & Lloyd 1898). Canada balsam has been reported to produce dermatitis when used in perfumery (Greenberg and Lester 1954). A laboratory worker who was sensitised in her work to Canada balsam showed positive patch test reactions to Canada balsam and to lavender oil (Lavandula, fam. Labiatae), eucalyptus oil (Eucalyptus, fam. Myrtaceae), clove oil (Eugenia, fam. Myrtaceae), balsam of Peru (from Myroxylon balsamum Harms, fam. Leguminosae), styrax (Liquidambar fam. Altingiaceae) and to eugenol, isoeugenol, nerolidol and farnesol (Rudzki and Kielak 1972).
A florist developed contact dermatitis from the foliage of balsam fir; a patch test produced a positive reaction (Kappes 1948).
In a study of 82 cases of eczematous hand dermatitis in Oregon, USA, extracts of the foliage and the bark of the grand fir produced positive patch test reactions in one case, a carpenter with a lifelong history of atopic dermatitis who also reacted to an extract of the wood of the Douglas fir (Suskind 1967).
This species yields Siberian Pine Oil (more correctly known a Siberian Fir Oil), which may be used as a rubefacient (Wren 1975).
These evergreen trees occur naturally from North Africa to Asia. Four species are recognised, but according to some authorities there are just two species, one comprising several geographical variants (Mabberley 1997):
Other botanical species which are commonly named cedar are Libocedrus and Thuja.
Handling the wood or cones and contact with the odorous gummy sap of these trees is likely to cause irritation of the skin of wood cutters, foresters and carpenters (Chopra et al. 1958). Wood cutters who saw timber from these trees are liable to dermatitis (Behl et al. 1966).
Cedrus deodara, in India, provides a turpentine which can cause dermatitis (Behl et al. 1966).
The native cedar of the United States named as a source of dermatitis (Weber 1953) probably refers to Thuja.
The wood dust of cedar of Lebanon can produce asthma (Greenberg 1972).
Ten or twelve species are found in Europe, northern Asia and North America.
Tenchio (1948) noted the presence of lichens and liverworts (Frullania) on larch trees. These are responsible for woodcutter's eczema.
Three botanical varieties of Larix decidua are recognised:
However, it is likely that all reports in the European dermatological literature that refer to "larch" without specifying a botanical name refer to the taxon Larix decidua Mill. var decidua.
A furniture-maker developed occupational urticaria from larch wood dust. The dust concentration during the grinding of the wood in the mill exceeded 10 mg/m3. Epicutaneous tests to larch veneer and to a petroleum ether extract of untreated larch wood produced positive results. Limonene, α-pinene, β-pinene and Δ-3-carene were demonstrated in the extract (Hanslian and Kadlec 1964). A scarlatiniform eruption was attributed to ingestion of Venice turpentine which is derived from this species (Angus 1913).
Larix leptolepis was listed as an irritant wood capable of producing dermatitis (Orsler 1973).
The bark of Larix americana, which has astringent properties, has been used in folk medicine to prepare an external application for haemorrhoids (Wren 1975).
50 species are found in north temperate regions especially in eastern Asia.
Dermatitis from spruce was mentioned by White (1917). Splinters irritate the skin whilst workers who cut up "silver spruce" wood and women who sanded it developed vesicular and bullous dermatitis (Prosser White 1934). In a sawmill worker who had asthma, intradermal tests to spruce and pine (Pinus) produced positive reactions, negative in controls (Bahn 1928). An instrument maker who had dermatitis of the hand showed positive patch test reactions to spruce and casein glue (Woods and Calnan 1976).
Contact sensitivity to balsam of Pine (Pinus) or spruce was found in 5.5% of 1247 patients; the majority reacted to both balsams. Many of the patients were also contact sensitive to balsams of Tolu and Peru (see Myroxylon balsamum Harms, fam. Leguminosae), storax (Liquidambar) or benzoin (Styrax). Only in a minor number of cases could exposure to oil of turpentine and rosin (colophony) (Pinus) be held responsible. Hydroxystilbenes which have been isolated from balsam of pine were postulated as the sensitising agents (Fregert and Rorsman 1963). Persons contact sensitive to balsam of Peru, balsam of pine (Pinus) and balsam of spruce are often contact sensitive to diethylstilboestrol and nearly all persons sensitive to the latter are sensitive to the balsams (Fregert and Rorsman 1960). Some coumarins are related to oestrogenic substances (Soine 1964).
35 of 712 patients showed positive patch test reactions to a mixture of balsams of spruce and pine, 15% of each. In 12 of the 35 patients, contact sensitivity to the balsams were considered to be the main or a contributory cause of hand eczema. The sources of exposure were considered to be handling spruce and pine twigs and freshly cut pine trees, wood-working, florists' work, handicrafts and dressing Christmas trees (Agrup 1969). Dermatitis from balsams usually arises from therapeutic use of popular medicaments; cross-sensitivity with balsam of Peru is frequently observed (Hjorth 1961).
This species provides a commercially valuable timber known as deal, white deal, or whitewood. It is also widely grown for the traditional Christmas tree trade.
Using Picea vulgaris as an example, Pereira (1835) noted that in "Coniferae we find the different species pervaded with an oleo-resinous juice, in consequence of which they possess stimulant properties." Schulmann & Détouillon (1932) noted that they had observed dermatitis attributable to "sapin de Hongrie" — Hungarian fir, which is possibly this species — in two wood-workers.
White (1887) noted that the resin which exudes from this tree is named Burgundy pitch. When applied to the skin in the form of a plaster and worn for varying periods, the plaster causes redness, itching papules and on delicate skins, even pustules and ulcers. The Norway spruce is the source of Jura turpentine (Felter & Lloyd 1898).
Two asthmatic patients became sensitive to the needles on their Christmas trees; intradermal tests with a saline extract of the needles produced positive reactions (Cobe 1930).
Amber has long been regarded as a fossiised tree resin produced by this extinct member of the Pinaceae. However, more recent analyses (Wolfe et al. 2009) have revealed that it is probably derived from extinct members of the family Sciadopityaceae, the only living representative of which is Sciadopitys verticillata Siebold & Zucc. (syns Pinus verticillata Siebold, Taxus verticillata Thunb.), the Japanese umbrella pine.
According to Felter & Lloyd (1898), crude oil of amber (Oleum Succini Crudum) is obtained by destructive distillation of amber as a by-product in the preparation of succinic acid from this source. Rectified oil of amber (Oleum Succini Rectificatum) is prepared from oil of amber by steam distillation followed by separation of the distilled oil from the water. Applied externally it is a rubefacient, having being used to prepare liniments such as Linimentum Succini Compositum and Roche's Embrocation.
Karlberg et al. (1992) studied the dermatitic properties of Baltic amber. They concluded that the resin acids abietic acid and dehydroabietic acid present in Portuguese colophony could also be detected at low levels a diethyl ether extract of Baltic amber. Coarsely ground amber suspended in petrolatum caused positive patch test reactions in patients with contact allergy to colophony. Furthermore, guinea pigs sensitised to colophony showed positive reactions to amber, but animals induced with amber did not react when challenged with amber. A use test with an amber necklace in two patients with positive test reactions to amber and colophony was negative, this supporting the view that amber in personal ornaments is not a clinical problem.
Workers with amber, particularly myopes who bend low over their task, may develop a yellow corneal staining with some irritation due to an encrustation with minute particles of the hard resin (Duke-Elder & MacFaul 1972b).
Amber Extract & Amber Powder [INCI; CAS RN 9000-02-6]a are recognised cosmetic product ingredients purported to have hair conditioning, skin conditioning, and deodorant properties (Standing Committee on Cosmetic Products 2019, CosIng 2020).
Between 70 and 100 species are found in north temperate regions and on mountains in the northern tropics.
Although species of this genus are extensively cut for wood and resins, dermatitis in forest-workers appears to be uncommon. Two of 125 forest-workers who had dermatitis showed positive patch test reactions to an acetone extract of pine wood (Mitchell 1970). Shavings of the wood produced dermatitis in wood-workers (Peri 1910). Workers can develop dermatitis from the oil of pine chips used for making rope (Schwartz et al. 1957).
Five carpenters who had contact dermatitis showed positive patch test reactions to pine wood sawdust and extracts (Wilkinson, D.S. 1973, Personal communication to Mitchell JC). It is not known whether the sensitiser is a stilbene such as pinosylvine (King 1953), Δ-3-carene as in turpentine or some other compound. Woodcutter's eczema from pine trees is caused by lichens or liverworts (Frullania) on the bark.
Dermatitis occurred in foresters working on pines infested with a caterpillar (Thaumatopoea pinivora). Patch tests to the caterpillar hairs produced positive reactions, negative to the pulped cocoon (Katzenellenbogen 1955). Some caterpillar hairs are irritant.
Woods and Calnan (1976) reported six wood-workers who had dermatitis and positive patch test reactions to deal or pine. Pinus sylvestris is known as red deal. In one of them, positive patch test reactions were observed to pinosylvin, anthothecol, colophony, formalin and turpentine. Two also reacted to teak (Tectona grandis L.f., fam. Labiatae), one of these to lapachol and to anthothecol.
[Information available but not yet included in database]
Three cases of contact dermatitis from this wood were reported by Burry (1969).
The wood is used in Australia in the building industry, for box making, as fencing posts and in furniture manufacture. Nine male patients developed dermatitis from exposure to the sawdust, the wood or the tree. Four were reactive to adhesive plaster, three to wood turpentine and one to colophony (Burry 1976).
Schulmann & Détouillon (1932) noted that they had observed dermatitis attributable to "pin sylvestre" in two wood-workers. Three cases of contact dermatitis from this wood - in two workers in wood-yards and in a messenger in a wood research establishment - were observed by Wilkinson (1973, Personal communication to Mitchell JC).
Derivatives of Pinus can produce dermatitis. Contact sensitivity to Balsam of Pine is noted under Picea.
Exacerbation of turpentine dermatitis occurred in a painter after he ate sweets made from pine buds (Jadassohn 1960).
A joiner's mate who had eczema of the hands was found to show positive patch test reactions to dry and moist pine dust and to colophony resin (Beer 1970).
Pine wood extract, applied as a topical remedy for ringworm of the toes, produced dermatitis (Goodman 1933).
Sources of turpentine are recorded by Usher (1974):
Turpentines derived from different geographical locations can vary in their chemical composition. Fresh turpentine can vary in chemical composition from aged turpentine (Anon 1971).
Garland (1886) reported a case of contact dermatitis from turpentine applied for a sprained wrist followed by recurrence at the contact site (focal flare) and partially generalized dermatitis after ingesting turpentine for treatment of bronchitis. Dermatitis of the face from turpentine used by painters to clean pallets and brushes was reported by White (1887). Oil of turpentine has long been used as a rubefacient.
Early reports of dermatitis from turpentine were reviewed by Prosser White (1934).
Pirila (1968) provided the following information:
Oil of turpentine is a variable mixture of numerous terpenoid compounds and is derived from various sources; for instance, from the balsam of pine trees and as a by-product in the manufacture of sulfate cellulose. The main components, 2-pinene (= α-pinene), 1-pinene (= β-pinene), 3-carene (= Δ-3-carene), and dipentene (d- and l-limonene) are monoterpenes, which have a common chemical formula C10H16, but different structures.
Practically all oils of turpentine contain large amounts of 2-pinene. On the other hand, the 3-carene content varies in the different types, being high (30-40 percent) in most sulfate oils and low or negligible in many balsam oils, e.g. French oil of turpentine.
The Finnish oils of turpentine, mostly sulfate oils, contain large amounts of both 3-carene and 2-pinene. 3-carene has been shown and convincingly confirmed by us to have a stronger eczematogenic effect than the other terpenes. Moreover, 3-carene is much more rapidly oxidized than the other terpenes. The easier oxidizability of 3-carene is in good conformity with our observation that the addition of small amounts of this terpene markedly increases the eczematogenic effect of the others. This phenomenon explains also most of the positive reactions we obtained with different commercial brands of 2-pinene containing minute amounts of carene only.
However, not all the positive reactions to other terpenes appeared to be due to carene impurities. Therefore, with the earlier observation that the eczematogenic effect of 3-carene depends on its hydroperoxide content as a basis, we compared the degree of sensitivity to different terpenes in a total of 106 patients sensitised to oil of turpentine. The more the other terpenes were purified of 3-carene, the lower, as a rule, were the eczematogenic effects of their oxidation products. The sole obvious exception was 2-carene, which was included in the study since it presumably has hydroperoxides in common with 3-carene. On the other hand, positive eczematous reactions to the other terpenes were obtained in a few cases only. Thus, four of forty-five patients tested with sufficiently purified samples of 2-pinene and one of sixteen patients tested with limonene reacted only at test concentrations 20 times higher than the threshold for 3-carene. In these cases the reactions to 2-pinene and limonene have to be considered specific. Moreover, some of the other reactions may be due to weak but specific sensitivity to 2-pinene, 2(10)pinene or limonene. However, in the majority of our cases the hypersensitivity was obviously directed towards 3- and 2-carenes alone, or more accurately, in our opinion, towards one or more carene hydroperoxides.
Since several hydroperoxides of 3- and 2-carene are, at least theoretically, common to both and since the Finnish oils of turpentine do not contain significant amounts of 2-carene, it is reasonable to conclude that the reactions to the latter are due to some of their common hydroperoxides. On the other hand, the chemical structures of the other terpenes differ so much from that of 3-carene that they cannot be expected to have any hydroperoxides in common. Moreover, since sensitivity to other terpenes than carene was the exception rather than the rule and always weaker than to 3-carene, true cross-sensitivity does not appear probable; but simultaneous, independent sensitisation to different terpenes may preferably be considered. The almost negligible role played by terpenes other than 3-carene in Finland can be attributed both to the markedly stronger eczematogenic effect of 3-carene and to the predominant exposure to its hydroperoxides as a result of the considerable carene content of the Finnish oils of turpentine and of the rapid oxidation of 3-carene.
The patterns of sensitivity to different terpenes can be expected to vary according to the exposure. In fact, in a subject experimentally sensitised to French balsam oil of turpentine containing small amounts of 3-carene only, the sensitivities to 2-pinene and 3-carene were of approximately equal degree. Furthermore, the pattern appears to be different elsewhere; for instance, in Germany (Grimm and Gries 1967). Therefore, a comparative study, with the same test substances, would be advisable among patients from areas where different types of oil of turpentine are used. However, even as such, our results allow conclusions on the specificity and patterns of hypersensitivity to different terpenes.
This subject was reviewed by Pirila et al. (1969). The incidence of turpentine contact dermatitis has declined in countries where legislation has resulted in the substitution of other solvents.
Colophony (rosin) is derived principally from Pinus palustris.
Rosin (colophony, abietic anhydride) is the residue left after distilling off the volatile oil from the oleoresin obtained from Pinus sylvestris and other species. Rosin occurs as wood rosin obtained from pine stumps: gum rosin is the exudate from incisions in the living trees, Pinus palustris and P. caribaea: Tall oil (liquid rosin) - is a by-product of the wood pulp industry. (Tall is a Swedish name for pine). Rosin is chiefly produced in the United States. Its constituents are about 90% resin acids and 10% neutral matter. Of the resin acids about 90% are isomeric with abietic acid; the other 10% is a mixture of dihydroabietic acid and dehydroabietic acid. Rosin oil is obtained by dry distillation of rosin.
Ester gums are combinations of natural resins (such as rosin) with glycerine. Emulsions of acid ester gums may be used as fabric finishers and produce allergic contact dermatitis from clothing. The probable main sensitising agent in such a finish was abietic acid or one of its derivatives (Schwartz et al. 1940). Although this paper has been frequently cited, abietic acid was not actually proven allergenic.
Rosin produced contact dermatitis in a violinist (Ramirez and Eller 1930). Rosin in hair lacquer and adhesive plaster caused dermatitis (Greenberg and Lester 1954). Colophony gave positive patch test reactions in 6/16 persons contact sensitive to adhesive plaster (Jirasek and Kvicalova 1965). 19 of 712 persons (250 males and 462 females) tested showed positive patch tests to colophony. In 13 of the 19 cases, allergy to this material was considered to be the main cause or a contributory cause of hand eczema. Products most often suspected as causative were adhesive tape, furniture polish and saw-dust (Agrup 1969).
Fregert et al. (1969) gave the incidence of sensitivity to colophony in various European Eczema Clinics.
Six patients in a spinal injuries centre showed positive patch test reactions to colophony (Walshe 1975); she discussed the sources of exposure. Physiotherapy wax contaminated with colophony produced dermatitis (Hambly and Wilkinson 1975). 5 of 306 patients with leg ulcers were contact sensitive to colophony (Angelini et al. 1975). Colophony rosin applied to a belt to increase friction produced dermatitis in an engineer (Wilkinson and Calnan 1975). Colophony in soap may have caused dermatitis (Cooke and Kurwa 1975). A pre-wash dirt remover used on a collar produced dermatitis of the neck. The remover contained colophony. The patient was patch test positive to colophony and rosin powder (Kirk 1976).
Wood tars are obtained by the destructive distillation of the woods of various botanical species (e.g. pine (Pinus), beech (Fagus), birch (Betula) and juniper (Juniperus)). Such therapeutic tars are refined to a lesser or greater degree. Pine tar contains many substances present in colophony (rosin) so that these products can give concomitant reactions.
Positive patch test reactions to wood tars are of importance in directing attention to many other substances encountered in daily life. In 1831 consecutive patients with dermatitis, 88 (4.8%) showed positive patch tests to wood tars. 35 per cent of patients sensitive to wood tars were also sensitive to perfumes of popular toilet soaps and detergents (Hjorth 1965).
Wood creosote derived from wood tar differs in composition from coal tar. Application of Burgundy pitch (otherwise known as Pix Burgundica) derived from Pinus abies has been reported to produce "a troublesome inflammaion of a pustular and vesicular character" and an "eczematous eruption" (Piffard 1881).
α-Pinene in Boot Polish
Boot polish may consist of a mixture of paraffin wax, carnauba wax (from Copernicia prunifera H.E.Moore, fam. Palmae), modified Montan wax (obtained from lignite), a microcrystalline wax a dye (nigrosine in the case of black polish) and two solvents white spirit and α-pinene. The last named produced a positive patch test in a patient who was contact sensitive to boot polish (Hindson 1972). A perfume compound (Violet 3567) caused allergic contact dermatitis from shoe polish (Broughton 1969). Ekblad (1956) placed shoe polish at the head of his list of eczematous sensitisers and stated that one particular brand was usually the offender; it seems likely that he was patch testing at an irritant concentration.
Pine pollen, which has acid-fast staining characteristics similar to those of the tubercle bacillus, has been suggested for a role in the aetiology of sarcoidosis (Cummings and Hudgins 1958). They investigated several species identified only by common name. The hypothesis seems dubious (Scadding 1967).
Pine pollen has been suspected of causing hayfever (Wodehouse 1971).
Paper is obtained from pine trees and from other species. The pulp undergoes many processes of purification during which tars, oils and resins are separated. Allergic contact dermatitis can occur from exposure to pine tar, colophony and essential oils (Schwartz et al. 1957). Various chemicals are added to the refined product according to the requirements of the finished paper. Irritation from alkalis, calcium bisulphite, sodium hydroxide and other chemicals can occur. Paper which has been sized by resin caused contact dermatitis of the hands; abietic acid and resins containing colophony were implicated by patch testing (Wikstrom 1969). Paper containing formalin did not produce positive patch test reactions in persons contact sensitive to formaldehyde (Fisher et al. 1962).
In a study of 82 cases of eczematous hand dermatitis in Oregon, USA, one patient reacted when patch tested with an extract of the wood of the Douglas fir, and one reacted to an extract of the needles. In the first of these cases, his contact dermatitis was considered to be at least in part provoked by woods such as Douglas and grand fir, Abies grandis Lindl. (see above). In the other case, a connection between the patch test reaction to Douglas fir foliage and his dermatitis could not be established. In preliminary studies, a diethyl ether extract of the wood of the Douglas fir, but not an ethyl acetate extract or an acetone extract, had exhibited a high degree of sensitising activity in guinea pigs (Suskind 1967).
A messenger at the Forest Products Research Laboratory with slight exposure to many woods developed severe dermatitis of the exposed skin. Patch test to Douglas fir produced strong positive reactions, negative to several other woods (Wilkinson, D.S. Pers. comm. 1973).
Trade complaints are received of septic splinter wounds (Orsler 1973, Nordin 1947). Neudorffer (1902) reported a case of general symptoms after wreath making with Douglas fir. The wood yields α-pinene and Δ-3-carene (Hancock and Swan 1965).
According to Remington et al. (1918) and Felter (1922), this species is the source of Canada pitch, otherwise known as hemlock pitch or Pix Canadensis, and a volatile oil known as Oil of Hemlock or Oil of Spruce. Its bark has been much used for tanning, an extract being made for the purpose. Canada pitch has been employed medicinally as a gentle rubefacient; the oil has been used as an embrocation for painful and swollen parts.
Describing the production of Canada pitch from this species, Remington et al. (1918) note that in trees that have attained their full growth and have begun to decay, juice exudes spontaneously and hardens upon the bark in consequence of the partial evaporation or oxidation of its volatile oil. The bark thus incrusted is stripped from the tree, broken into pieces, and boiled in water. The pitch melts, rises to the surface, is skimmed off, and is still further purified by a second boiling in water. Hemlock pitch is hard, brittle, quite opaque, of a dark reddish-brown color, becoming still darker by exposure to the air, of a weak peculiar odor, and scarcely any taste. It softens and becomes adhesive with a moderate heat.
White (1887) noted that the resin that exudes from "Abies canadensis Hemlock Spruce", known as Canada pitch, when applied to the skin as a plaster, can produce redness, itching, papules, and even pustules and superficial ulcers. One of 125 patients who had dermatitis showed a positive patch test reaction to a commercial acetone extract of "Hemlock-Spruce" (Mitchell 1970).
Tsuga Canadensis Bark Extract / Leaf Extract / Leaf Oil / & Oil [INCI] are recognised cosmetic product ingredients variously purported to have skin conditioning, skin protecting, and masking properties (Standing Committee on Cosmetic Products 2019, CosIng 2020).
Historically, there has been much taxonomic confusion in relation to the application of the common name hemlock spruce (Farwell 1914). It is possible that this species, Tsuga canadensis, has been confused with the white spruce or Canada spruce, Picea laxa Sarg. (syns Abies canadensis Mill., Picea glauca Voss, Pinus canadensis Du Roi), for which the common name hemlock spruce has also been used. Picea laxa is widely distributed in Canada and Alaska, and in northern states of the USA, its distribution seemingly fitting better with the description in the US Dispensatory — see Remington et al. (1918) — of the geographic distribution of the tree species that is the source of Pix Canadensis: "abundant in Canada, Nova Scotia, and the more northern parts of New England, and is found in the elevated and mountainous regions of the Middle States" than does the distribution map provided in the USDA Plants Database for Tsuga canadensis Carrière (syn. Abies canadensis Michx.). It is also possible that the Eastern hemlock spruce, Tsuga canadensis, has been confused with the Western hemlock spruce, otherwise known as Alaskan pine, Tsuga heterophylla Sarg.
This tree is said to cause dermatitis (Orsler 1973). A diethyl ether extract of wood from a tree identified only as "hemlock" growing in the forests of Oregon, USA (but probably this species) exhibited a high degree of sensitisation in guinea pigs (Suskind 1967).