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The 60 genera comprising some 600 species of trees and shrubs are distributed throughout he tropics, and are also found in warm temperate regions of Europe, eastern Asia, and the Americas.
Many species have been widely cultivated beyond their limited areas of origin because of their economic importance as sources of timber, lacquer, oil, wax, dye, and for their often edible fruit or nuts. The most important fruit is the mango from Mangifera indica L., whilst the most important nut is the cashew from Anacardium occidentale L. Dyes may be obtained from the leaves of Rhus copallina L. (syn. Schmalzia copallina Small), the wood of Rhus cotinoides Nutt. (syn. Cotinus americanus Nutt.), the roots of Rhus glabra L., the galls of Rhus semialata Murray (syns Rhus chinensis Mill., Rhus javanica L.), etc. Because of the tannin content of the leaves or bark, several species including Rhus abyssinica Hochst., Rhus albida Schousboe, Rhus copallina, and Rhus coriaria L. have been utilised for tanning (Usher 1974).
The fruits of certain species of Rhus L. have been used by American Indians to make a drink. Indian lemonade is prepared from Rhus typhina L.; Rhus aromatica Aiton (syns Rhus canadensis Marshall, Schmalzia aromatica Desv.), Rhus copallina, and Rhus glabra may also be utilised in this way (Usher 1974).
Rhus typhina L., the stag's horn sumach, makes a quite attractive ornamental shrub and is often grown in gardens. A few other species of Rhus may be encountered more rarely, as may Cotinus coggygria Scop., the smoke tree.
Plants of the family Anacardiaceae are probably the most common single cause of contact dermatitis in man. The skin reaction occurs following sensitisation to various alkyl- catechols, phenols, quinols, and resorcinols. At high concentrations, these compounds are also primary irritants.
- Anacardium L.
The 15 species of this genus are natives of tropical America. Some, particularly A. occidentale L., are widely cultivated throughout the tropics.
- Anacardium excelsum Skeels
- (syns Anacardium rhinocarpus DC., Rhinocarpus excelsa Bertram)
This tree provides timber (Hausen 1981), but Woods & Calnan (1976) found no reference to dermatitis from it.
- Anacardium occidentale L.
- (syn. Cassuvium pomiferum Lam.)
- Cashew-Nut Tree, East Indian Almond, Jambu Gajus, Jambu Golok, Keterek, Marãnón, Jocote Marãnón
This species is a native of Brazil but is cultivated in many parts of the tropics. The tree is grown principally for its nuts, but is also important for the oil obtained from the nut shells (cashew nut shell liquid), and its gum. Its timber, known as acajou (as also is the timber of various species of Swietenia Jacq. and Khaya A.Juss. in the family Meliaceae), is used for house and boat building in South America but is not exported (Hausen 1973).
Principally from studies of cashew nut shell liquid, this species has been found to be a source of a wide variety of irritant / allergenic alk(en)ylphenols Anacardic acid (a mixture of 2-carboxy-3-alk(en)ylphenols), cardanol (a mixture of 3-alk(en)ylphenols), and cardol (a mixture of 5-alk(en)ylresorcinols), together with a series of less thoroughly investigated 2-methyl-5-alk(en)ylresorcinols may be involved as primary and secondary contact allergens, and also as primary irritants (Evans & Schmidt 1980).
The bark of the tree contains a thick, resinous, acrid sap which blackens on exposure to the air. The wood exudes a yellow gum, named cashawa gum or gomme d'acajou, which can blister the skin. The yellow or red cashew apple (technically a swollen peduncle) contains a juice that is astringent until the fruit is ripe, when it is acid but edible. The apple is the receptacle of the true fruit — the cashew nut. This nut is lightly attached to the apex of the apple, and attains its full size before the receptacle enlarges to form the apple. The apple is thus a false fruit. Between the smooth outer shell and the inner shell of the nut is a fibrous pulp containing a sticky brown oil - cashew nut shell liquid. This is caustic and sensitising. The kidney shaped kernel is the cashew nut of commerce and is innocuous unless contaminated with the shell oil, in which case it will appear blackened. As with other nuts, the kernel contains a fixed oil resembling almond oil (Prunus amygdalus Batsch, fam. Rosaceae). This is termed cashew oil or anacardic oil. Ambiguity may arise between the the use of the terms cashew oil and cashew nut shell liquid (Morton 1961).
The distribution of irritants and sensitisers in the various parts of the tree is such that any person from the woodcutter to the consumer of cashew nuts is at risk. For the nut addict, however, the risk is indeed small.
The cashew apples with nuts attached fall from the trees when ripe. The nuts are processed to obtain the kernels, together with cashew nut shell liquid as a by-product. One method involves roasting the nuts on an open fire to dispel some of the caustic oil. The fumes from such fires are irritating to the eyes, nose, throat, and skin. When roasted, the nut shells are split open and the nuts removed (Morton 1961). Mechanisation allows the nuts to be obtained from the unroasted nuts and hence increases the quantity of nut shell oil available for subsequent sale.
The nut shell oil will blister the skin on contact (Morton 1958). It is used in indigenous medicine as a rubefacient and vesicant (Morton 1961). Nadkarni (1976) recorded that in Indian traditional medicine, the juice of the nut is used as a substitute for iodine locally whilst the oil obtained from the shell by maceration in spirit is applied to cracks of the feet. He also noted that the fruit is useful as an anaesthetic in leprosy and psoriasis, and as a blister in the treatment of warts, corns, and ulcers. Wren (1975) noted that the fresh juice of the shell is acrid and corrosive, and that West Indian negroes use it for warts and corns.
The nut shell oil also has many industrial uses, including use in the manufacture of brake linings. It has been used as a preservative for fishing lines and as an insect repellant in book bindings. A dilute extract has been used as a gloss on vanilla pods (Vanilla Mill. species, fam. Orchidaceae), and has been held responsible for "vanilla itch" in workers handling the treated beans. Both the sap of the tree and the oil can be used for marking cloths, but are considered less of a dermatological hazard than marking nut oil from Semecarpus anacardium L. The gum is used as a varnish to protect books and woodcarvings from insects, and also as a substitute for Gum Acacia (from Acacia senegal Willd. and related species, fam. Leguminosae) in adhesives (Morton 1961).
The fact that dermatitis may result from contact with cashew nut shells has undoubtedly been known for a very long time in regions where the tree grows naturally. Perhaps the earliest record is that of De Préfontaine (1763). Over a hundred years later, Lewin (1882) recorded a case described by Schwerin (undated) of a woman who put one half of a "bean" in her ear to relieve a toothache and pain in the face. She developed oedema of the ear, eyelid, cheek, and neck. Lewin (1882) also described a case where a "bean", divided longitudinally, was placed upon a string hung around the neck in such a manner that it lay over the manubrium sterni. Two days later, vesicular dermatitis appeared on the upper anterior trunk.
Those felling the trees may suffer an irritant dermatitis (Hausen 1973); such a case has been described where the sap caused a localised lesion of the skin on a farmer's chest (Bedi 1971). An additional hazard occurs when the tree is infested with caterpillars having irritant hairs. Biting the unripe apples can cause a primary irritant dermatitis around the mouth (Bedi 1971). The cashew apple may also elicit a different reaction - Strobel et al. (1978) described a case where perioral dermatitis resembling herpes occurred in a female who had eaten an unpeeled cashew apple. The ulceration took more than 10 days to resolve.
Workers on cashew nut farms may develop an acute dermatitis resembling that commonly observed in sensitised persons, but sometimes the only lesions are roughness, cracking, and irritation of fingers and hands (Behl et al. 1966, Cueva 1965). This chronic dermatitis afflicts particularly those employed in removing the kernels from roasted nuts (Morton 1961). Unprocessed nuts were responsible for dermatitis amongst dock workers who unloaded them, and also in a secretary and chemist who handled them (Downing & Gurney 1940). Roasted cashew nuts sold as ornaments or as heads of "swizzle sticks" used for stirring drinks have caused dermatitis because they had been inadequately roasted and oil had seeped through the shell (Morton 1961).
Nine workmen developed dermatitis after dipping electrical equipment in a commercial varnish containing raw cashew nut shell liquid (Lockey 1944). One of the nine developed exfoliative dermatitis and severe anaemia, haematuria, and prostration. Occupational dermatitis from cashew nut shell liquid was discussed by Schwartz et al. (1945).
Small amounts of the urushiol transferred from the shell to the nuts during shelling produced dermatitis when the fresh nuts were ingested in large amounts by five Toxicodendron Mill. sensitive individuals. Antigenicity disappears in a few days so that "stale" raw cashews like the commercially available dry roasted variety are harmless (Ratner et al. 1974).
The occurrence of cross-sensitivity between the urushiols of poison ivy (Toxicodendron radicans Kuntze) and those of cashew nut shell liquid has long been recognised (Keil et al. 1945a, 1945b).
- Astronium Jacq.
The 15 species in this genus are native to Central and tropical South America, and the West Indies.
- Astronium fraxinifolium Schott
- Tigerwood, Zebrawood, Gonçalo Alves
The heartwood of this species is a minor timber of commerce (Hausen 1981). The sawdust sometimes causes such intense skin irritation that the affected areas resemble second degree burns (Freise 1932).
- Astronium graveolens Jacq.
The wood often resembles that of Dalbergia L.f. species (fam. Leguminosae) and may be mixed with shipments of them (Record & Hess 1943).
- Blepharocarya involucrigera F.Muell.
- Bolly Gum, Northern Bolly Gum, North Queensland Bollygum, Rose Butternut
North Queensland forest officers are unanimous in stating that the wood is poisonous if rubbed on the skin (Cleland 1943).
Mitchell & Maibach (1977) noted the absence of cross-sensitivity to the dried leaves of this species in patients sensitive to poison ivy (Toxicodendron Mill. spp., fam. Anacardiaceae). Three patients out of 39 tested did however show 1+ reactions to the leaves; these reactions were judged to be irritant.
The genus Blepharocarya F.Muell. comprises just two species of trees found in north-eastern Australia. The genus has been classified in its own family by some authorities, namely the Blepharocaryaceae.
- Buchanania Spreng.
The 25 species are natives of Indo-Malaysia and tropical Australia.
Burgess (1966) states that the black sap of Buchanania species is said to be non-irritant.
- Buchanania lucida Blume
- (syn. Buchanania florida Schauer)
- Sparrows' Mango, Katak Udang, Ketak Udang, Otak Udang, Pauh Pipit, Puan, Terentang Tikus
The juice of this species was noted by a plant collector to produce itching (von Reis Altschul 1973).
- Campnosperma Thwaites
Some of the 15 species in this genus, which occurs throughout the tropics, are known in Malaya to produce dermatitis (Kochummen 1972). Corner (1952), referring to three species found in Malaya, states that they contain a slightly resinous sap which is harmful to some persons, especially that which oozes from the wood.
- Campnosperma auriculata Hook.f.
- Terentang, Serentang
The wood sap of this tree may cause dermatitis in some persons (Corner 1952, Burgess 1966). The oily exudate from this tree contains long chain alicyclic keto alcohols, together with small quantities of alkylquinols of which nonadecylquinol has been identified (Lamberton 1959a).
- Campnosperma brevipetiolata Volkart
In New Guinea, an oil (known as tigaso oil) obtained from this species has been used, sometimes mixed with soot, as an application to the body in order to give protection from lice and fleas. A long chain alicyclic keto alcohol has been isolated from the oil (Dalton & Lamberton 1958), but no urushiols. The wood of Campnosperma coriaceum Hall f. also yields tigaso oil (Hou 1978).
- Campnosperma macrophylla Hook.f.
- Terentang, Serentang
- Campnosperma minus Corner
- Terentang Jantang
These species may cause dermatitis in some persons (Corner 1952, Burgess 1966).
- Comocladia P.Browne
The 20 species are natives of Central America and the West Indies. Oviedo reported (Standley 1927) that the Indian women of Santo Domingo used a vesicant paste made of the roots of Comocladia species to soften and lighten the skin of their arms and faces. In 1845, Williams (1845/46) drew attention to a report by Otto in the Gardeners Magazine of May 1842 of intensely severe oedema after minimal contact with the irritant sap of Comocladia species. Dahlgren & Standley (1944) note that the sap of some species causes blistering and prolonged inflammation similar to that caused by poison ivy (Toxicodendron radicans Kuntze) whilst Pardo-Castello (1933) notes that at least 17 of the 20 species are said to be capable of producing dermatitis.
- Comocladia dentata Jacq.
This species is among the 14 most common causes of plant contact dermatitis in the Dominican Republic (Brache & Aquino 1978). Lunin (1969) has also observed very many cases of dermatitis from this species on the steppes of Russia.
The timber, known as bastard brazil, is used locally for general purposes and can cause dermatitis (Standley 1927, Schwartz et al. 1957). The dermatitis may be persistent as the resin contaminates clothing and tools (Pardo-Castello 1962).
- Comocladia dodonaea Britton
- (syns Comocladia ilicifolia Sw., Ilex dodonaea L.)
- Christmas Bush
Oakes & Butcher (1962) note that this species has spiny leaves that can cause mechanical injury, and also sap that can produce severe dermatitis. It is among the 14 most common causes of plant contact dermatitis in the Dominican Republic (Brache & Aquino 1978).
- Comocladia domingensis Britton
This species are able to produce dermatitis (Brache & Aquino 1978).
- Comocladia engleriana Loes.
von Reis Altschul (1973) found an herbarium note stating that the plant contains a thick irritating juice … persons often being affecting just by passing the tree.
- Comocladia mollifolia Ekman & Helwig
von Reis Altschul (1973) found an herbarium note stating that the milky juice causes poison ivy-like dermatitis.
- Cotinus coggygria Scop.
- (syns Cotinus coriaria Duhamel, Rhus cotinus L.)
- Smoke Tree, Wig Tree, Venetian Sumach, Fustic Wood, Hungarian Yellow-wood
This species and its varieties are occasionally grown as ornamental shrubs for their brilliant leaf colouring in autumn (fall). The species occurs naturally from the Mediterranean to China.
The wood, when cut for veneers, and the sap have both been reported to cause dermatitis (Hausen 1970, Behl et al. 1966).
A yellow dye ("young fustic") may be obtained from the wood (Remington et al. 1918). The leaves were formerly used for tanning because of their high tannin content (Hurst 1942).
- Dracontomelon dao Merr. & Rolfe
- (syns Comeurya cumingiana Baill., Dracontomelon edule Skeels, Dracontomelon mangiferum Blume, Paliurus dao Blanco, etc.)
- Argus Pheasant Tree, Dao, Paldao, New Guinea Walnut, Pacific Walnut, Sekuan, Senkuang, Drachenapfel
This species is often referred to as Dracontomelum dao, a name of no botanical standing. It is the source of a timber that is used commercially for veneers and in the manufacture of fine furniture. No reports of ill effects in those who are exposed to the timber or its sawdust have been found.
Perry & Metzger (1980) note that in China, the fruit of this species is given as a depurative to cure dermatitis.