The α-methylene-γ-butyrolactones are part of a large and varied group of bioactive natural products widely present in plants. They have an α,β-unsaturated carbonyl system which allows the formation of covalent adducts with nucleophilic residues on diverse biomolecules which explains their high chemical reactivity. Most of them are of the sesquiterpene type (15 carbon atoms molecule) with an α-methylene group directed exocyclically to the γ-lactone ring. They are classified into six main groups of sesquiterpene lactone (SQL) structures: guaianolide, pseudoguaianolide, xanthonolide, ermophilanolide, eudesmanolide and germacranolide (Fig. 1). They are the predominant allergens in the Compositae family as well as in other related plant families such as Jubulaceae, Magnoliaceae, Winteraceae, and Lauraceae.1 The α-methylene-γ-butyrolactones can also be found as more simple structures in the Liliaceae (tulipaline A) and Alstroemeraceae families.

Figure 1.

Chemical structures of main groups of sesquiterpene lactones.

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The Asteraceae/Compositae family also referred to as the aster, daisy or sunflower family, comprise the second largest family of flowering plants in the world. It includes more than 22750 currently accepted species, spread across 1620 genera and 12 subfamilies. Over 200 species are important causes of contact dermatitis worldwide.2,3 This family presents a variety of edible plants, such as lettuce, chicory, dandelion, salsify, sunflower, scorzonera, artichoke and yacon. Many members are decorative flowers, such as chrysanthemums, gerbera, calendula, dendranthema, dahlias, and heleniums and many others are spread as common weeds. Also, species such as arnica, chamomile or feverfew are used medicinally. Asteraceae/Compositae can be recognized by its inflorescence consists of many tiny flowers clustered to form a flower head and subtended by an involucre.

SQLs are the predominant allergens although other compounds such as epoxythymol-diesters and polyacetylenes may also be involved.4 SQLs are usually lipophilic, and are often located in the liquid-soluble part (oleoresin fraction) of the leaf, stem flower and possibly in the polen.2,4,5 Although the mechanism of sensitization is unknown, several possibilities have been proposed: pollen or dry debris airborne transportation; direct and/or indirect contact with parts of the plant; as well as allergen inhalation or ingestion.4,6

Some peculiar cutaneous eruptions caused by Asteraceae/Compositae family have been described. The pseudophotodermatitis pattern occurs almost exclusively in middle-aged men with a history of outdoor exposure, being rare in children and women, although further studies have suggested an equal sex distribution.6,7 Exposed areas of the face, V of neck, hands and forearms are typically involved. In addition, non-clear-cut sun exposed areas such as retroauricular regions (“Wilkinson's triangle”), eyelids, nasolabial folds and under the chin are also involved, allowing its differentiation from a true photo-related dermatitis.7 In hot regions, during summer months dry dead plants material contributes to this airborne pattern of dermatitis. In USA, many compositae weed, including ragweed (Ambrosia spp.), induce this clinical pattern often called “ragweed dermatitis8 or “weed dermatitis” in regions where other composite weeds predominate, such as Ambrosia, Artemisia, Helenium, and Iva species.9,10 A similar pattern was described in Australia where it is known as “bush dermatitis” due to species such as Arctotheca, Cassini, Conyza, Cynara and Dittrichi11,12 and also in India where it is called “parthenium dermatitis” being the offending plant the Parthenium hysterophorus L.13,14 Although this environmental conditions are not normally encountered in the temperate regions of Europe, some isolated reports of airborne dermatitis (“ragweed dermatitis”) induced by feverfew (Tanacetum parthenium (L.) Sch. Bip.), chicory and lettuce, liverworts of the genus Frullania, and the chrysanthemums1,6,9 have exceptionally been reported.

A second special clinical pattern was described as atopic eczema-like eruption. Compositae allergy may be manifested as a generalized eczematous eruption with primarily flexural involvement. Although it most commonly occurs in elderly men in rural areas, cases in children have also been reported.4,15 An erythrodermic exfoliative pattern classically induced by weed Parthenium hysterophorus L. was also described. This plant was accidentally introduced in the west coast of India in contaminated seed wheat. Several thousands of cases of allergic contact dermatitis occurred, some of them fatal.16

Hand eczema is more frequent in women working in gardening after contact with weeds. A palmar distribution often predominates.17 Hand dermatitis is also associated with handling lettuce.18,19 Dermatitis confined to one or more localized areas such as facial dermatitis secondary to steaming chamomile tea or hand and arm dermatitis from herbal compresses20 has rarely been reported. Oral swelling, perianal pruritus and dermatitis of the trunk and arms were described in a sensitized drank chamomile tea patient.20 Stomatitis and throat swelling have occurred in some patients after eating lettuce and endivia.21 In one single patient erythema multiforme was reported to develop after patch testing.22

A rare chronic and disabling eccematous photodermatosis known as chronic actinic dermatitis (CAD), photosensitive dermatitis and actinic reticuloid has been linked to the ACD to compositae. A high incidence of allergic contact dermatitis to one or more allergens has been found among patients with CAD,23 and sesquiterpene lactones are commonly identified as allergens. It is thought that about 20%–75% of patients sensitized to Asteracea (Compositae) have some degree of photosensitivity. Thus, the progressive evolution of ACD to sesquiterpene lactones towards CAD has been postulated, but its origin is still unknown.

Patch Test

No ideal patch testing material to study Compositae induced dermatitis exists. Compositae family includes more than 1350 SQLs and almost 50% of them are potential contact allergens.2 SQLs with slight differences in molecular structure, may cause true cross-reactions, while identical SQLs from different species may be responsible of false cross-reactions. SQLs are not exclusive from the Compositae family and frequently show cross-reactions with other plant families. Because the concentration of SQLs shows seasonal and geographic variations and as cross-reactions between different species are not complete, when a patient is not tested with the relevant plants, the diagnosis may be easily overlooked.

Fresh plants or plant extracts should not be patch tested as them are. This procedure may cause severe contact reactions and can also elicit active sensitization. False positive irritant reactions or false negative results caused by low content of allergens (degradation products) can also occur.

In 1986, Benezra and Epstein developed the “sesquiterpene lactone mix” (SL mix) a non-sensitizing and seldom irritant mixture of three of the six main structural groups of sesquiterpene lactones (alantolactone, costunolide and dehydrocostuslactone of eremophilanolide, germacranolide and guaianolide group) (Fig. 2). This mixture allows to identify about 60% of SQL sensitization cases24 and was included in the European baseline series.17 Other studies19,25–27 reported different percentages, which can partly be explained by phytogeographical variations and the diversity of SQL structures.28 An alternative preparation, the Compositae mix, based on a mixture of plant extracts (arnica, yarrow, tansy, German chamomile and feverfew), detects a higher proportion of the cases, however, it may be irritant and cause patch test sensitization.29

Figure 2.

Structures of alantolactone, dehydrocostuslactone and costunolide, constituents of the SL mix test material.

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Dandelion and feverfew extracts, together or individually, also appear to be more useful than the SL mix.30,31 Other blends have been proposed, such as a mixture of Achillea millefolium L., Chamaemelum nobile All., Helianthus anuus L., Tagetes minuta L., and Tanacetum vulgare L. as well as extracts mixtures of arnica, German chamomile, feverfew, tansy, and yarrow.27

Jubulaceae Family (Liverworts)

Liverworts are non-vascular plants with a bryophyte life cycle. They comprise four genera: Frullania accounts for nearly 800 species, Jubula 15, whereas Steerea and Neohattoria are both montypic. These plants are often epiphytes growing on trunks and branches of trees or shrubs presenting a worldwide distribution, being rare common in tropical and subtropical regions and rare in frigid climates. They are often resistant to desiccation and direct light. Jubula species are largely confined to damp shaded rock surfaces.

At least 11 species of Frullania have been described as responsible of allergic contact dermatitis.32Frullania dilatata (L.) Dum. and Frulanina tamarisci (L.) Dum. have been frequently incriminated in Europe. Cases of allergic contact dermatitis were also described in the British Columbia (Canada), the Pacific North-West of the United States, and in the South-West of France.

The most important allergen is frullanolide,33–35 an α-methylene-γ-butyrolactone sesquiterpene from the eudesmanolide structural group. Other α-methylene-γ-butyrolactones have been reported as sensitizers such as oxyfrullanolide 5, cis-b-cycloscotunolide 6 and eremofrullanolide 7.35–37Frullania dilatata (L.) Dum. contains exclusively the d- or (+)-enantiomer of frullanolide while Frullania tamarisci (L.) Dum. exclusively yields the l- or (−)-enantiomer.36 Both enantiomers are sensitizers, and in guinea pigs the stereospecificity of sensitization to one enantiomer has been demonstrated 36,37 (Fig. 3).

Figure 3.

Chemical structures of d-(+)- and l-(−)-frullanolide.

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Sensitization to Frullania can occur by direct handling of trees or by airborne through volatilization of its small particles, especially during warm weather or by the action of chainsaws.34,35 Forester workers often suffer from “woodcutter's eczema” and domestic allergy can be presented in people who use lobe-leaved trees as firewoods. Exposed areas of skin are typically affected, with an “airborne” pattern on the face and the V of the neck. This clinical pattern can mimic a photosensitivity pattern but involving shaded areas such as the eyelids and nasolabial folds. The hands may become edematous, with involvement of finger webs but often sparing of the palms. Exceptional involvement of the genitalia and intertriginous folds has also been reported.38

Patch Test

Testing the patient with small pieces of Frullania is associated with a high risk of active sensitization. The SQL mix only detects about 1% of allergic reactions to Frullania. The frullanolide mix, a racemic mixture of (+)- and (−)-frullanolide at 0.01%, 0.033% and 0.1% in petrolatum39 is a safe and not sensitizing test, but only shows a 0.35% of positive reactions.

Testing the patient with small pieces of Frullania is associated with a high risk of active sensitization, however, it could be used if there is high clinical suspicion. Frullanolide mix, a racemic mixture of (+)- and (−)-frullanolide at 0.01%, 0.033% and 0.1% in petrolatum39 has been used in several clinical trials proving to be a safe and not sensitizing test, but with a lower sensitivity than the SQL mix. Therefore the allergen of choice in this cases is SQL mix, even thought it only detects 1% of the allergic reactions to Frullania.

Cross-reactions with botanically unrelated plants that contain similar allergens, e.g. Laurus nobilis L.,35Magnolia grandiflora L.40 and several Compositae may also occur.32,41,42

Liliaceae

Tulip genus which comprises 109 species of showy flowers is the most important genus of the Liliaceae family. A number of species and many hybrid cultivars are growing in gardens, used as pot plants or as fresh cut flowers. Most cultivars of tulip are derived from Tulipa gesneriana. Professional bulb growers, bulb collectors, sorters and packers are particularly at risk of contact dermatitis.

Tulip bulbs contain several glucosides including tuliposides A and B, which are weakly allergenic but are rapidly hydrolysed to tulipalin A and B. Tulipalin A appears to be the main sensitizer in clinical practice43 although tulipalin B also causes sensitization in guinea pigs44 (Fig. 4). Flowers, leaves and stems possess higher concentrations of tuliposide A than the bulbs; but sensitivity can develop from contact with any portion of the plant, although most of the cases occur in bulb growers who are continuously handling the bulbs. Contact with airborne allergens, although infrequent has also been reported.45

Figure 4.

Chemical structures of tulipalin A and B.

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The most common presentation is a combined allergic and irritant hand dermatitis known as “tulip fingers”. It is characterized by a painful, subungual and periungual erythemato-squamous, sometimes erosive lesions involving the fingertips, particularly the first and second fingers of the dominant hand.46 There may be fissures, suppuration and hyperkeratosis. The dermatitis may extend to the adjacent skin and rarely may involve distant areas or even give rise to a diffuse dermatitis.45,47 The dust in tulip sheds may induce conjunctivitis, rhinitis and asthma. Reaginic responses to tulip antigens can also occur.47

Alstroemeriaceae

These species have a cluster of tuberous roots and produce leafy stems, bearing one to several brightly colored flowers. Several species are found in special collections and only two species are widely distributed and produced: Alstroemeria aurantiaca D. Don, with orange flowers, who grows as a border plant, particularly in cottage gardens, and Alstroemeria ligtu (Peruvian lilies) which give rise to numerous colors, mostly in shades of lilac and pink, with darker veins and mottling on the petals (Fig. 5). They grow in Holland, South America, USA and Australia. Tulipalin A, the same allergen of the Liliaceae family, is the main responsible sensitizer, being found mainly in the petals and stem. The rate of sensitization for tulipalin A can exceed 50% in workers of Alstroemeria cultivation.48

Figure 5.

Alstroemeriaceae.

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Dermatitis most commonly affects florist who strip off the leaves manually and are therefore exposed to the broken plant with a high risk of allergic contact dermatitis. The lesions, in contrast to the “tulip finger dermatitis, can be more severe and tend to involve the fingertips of all digits of both hands. Occasionally, the clinical pattern can be very similar to that produced by the garlic clove (but in a bilateral and symmetric distribution).49 Workers who cut the flowers often show palm eczema.50–55 Airborne dermatitis56 and post-inflammatory depigmentation have rarely been reported.57 False positive responses due to a primary irritant reactions may also occur.58

The Anacardiaceae family also known as the “cashew family” or the “sumac family” is a very wide family of flowering plants. This family includes about 70 genera and 650 species of evergreen deciduous trees, shrubs, and woody vines. These plants are native from tropical and subtropical areas of the world, but some species occurs in temperate regions too. Members of the Anacardiaceae plant family that are important in dermatology include: the Toxicoendron genus, (common poison ivy, poison oak, poison sumac), Mangifera indica L. (mango), Toxicodendron vernicifluum (lacquer tree) and Anacardium occidentale L. (cashew nut).

Toxicodendron is the most allergenic genus of this family. It includes the poison ivy (Toxicodendron radicans Kuntze and subspecies such as T. radicans Kuntze var, rydbergii Erskine), the poison oak (Toxicodendron diversilobum Greene and Toxicodendron toxicarium Gillis), and the poison sumac (Toxicodendron striatum Kuntze, T. vernix Kuntze) complexes. These genera are the main causes of allergic contact dermatitis in the United States and approximately 50%–70% of the population seems to be sensitized.63

Occupational contact dermatitis to poison ivy is an important cause of occupational disability and contributes significantly to the monetary expense of the health system in the United States. Wilderness, rural and outdoor activities as well as outdoor occupations related to agriculture, forestry, and fire fighting, are at high risk of sensitization.64

The poison ivy dermatitis is generally unknown in Europe. The plants can be recognized by its compound leaves, with three or more smaller leaflets. Flowers and fruit arise in the angle between the leaf and the twig. The leaf stalk also leaves a “U”- or “V”-shaped scar after it falls off.65

The pentadecylcatechols, consisting of 1, 2-dihydroxy benzenes with a 15-atom side chain in the third position (3-pentadecylcatechol), also called urushiols are the sensitizers in the Toxicodendron plants. Urushiols are colorless or slightly64 yellow in their natural state, but they oxidize, polymerize and turn black when exposed to air. Urushiol is found in the stems, roots, leaves and skin of the fruits of these plants and also on fomites, where it retains its antigenic potential in the dry state indefinitely.66 Young leaves contain greater amount of urushiol than the older ones.67

Contact dermatitis primarily results from the direct contact with the oleoresin obtained from a portion of a bruised or injured plant. However, contamination and re-exposure to the antigen may occur, being the most important reservoirs the fingernails, clothing, animals, garden tools or firewood.10,68 Contact dermatitis usually appears within 2–4 days, however it may appear as late as 2 weeks after the history of contact. It is characterized by intense pruritus and an erythematous reaction followed by the appearance of multiple papules and vesiculo-bullous lesions in a linear distribution (Fig. 7). The face, neck, and genitalia are commonly affected and usually show intense oedema. The dermatitis has a self-limiting course, lasting approximately 1–2 weeks, but can last up to 6 weeks.64

Figure 7.

Erythematous linear arrays and erythema multiforme-like lesions on right elvow after contact with poison ivy.

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Other clinical presentations include erythema multiforme-like reactions,69 exanthematous and urticarial eruptions, and even renal damage that, may occur after accidental, medicinal or alimentary ingestion.70,71 Stomatitis and anal itch have been described after chewing the leaves or secondary to hyposensitization treatments. The “black spot poison ivy dermatitis” is a rare and very special condition, consisting of asymptomatic black lesions on the skin that cannot be washed off. These lesions are followed by subsequent pruritic papules and have been mistaken for melanoma in several cases.72

Ginkgo biloba L., the ginkgo tree, is the only representative of this family and is regarded as one of the world's oldest surviving tree species. Originating in southeastern China 200 million years ago, it was introduced to Europe during the early 18th century, and now it grows in temperate regions throughout the world. Contact dermatitis from the ginkgo tree is not due to its leaves but to its malodorous fruit exclusively borne in female trees.

The alkylphenols (anacardic or ginkgolic acids, cardols and cardanols) have been identified as the potential allergens. Ginkgolic acid 1, the most important allergen, is found mainly in the fruit, but can also be detected in Ginkgo leaves.89 Allergic reactions seem to occur only with open fruit extruding pulp. Handling the intact fruit is not harmful to sensitive persons.90

Contact dermatitis occurs especially in East Asians, who enjoy eating the “nuts” (seed kernels), and manipulate the seeds to remove the fleshy pulp and obtain the kernels. Pruritic, edematous and erythematous plaques with papules or vesicles appear on the hands, face, arms and anywhere the seed pulp is spread. Ingestion may also cause stomatitis and anal pruritus.91 While reactions are uncommon in the West, a small epidemic occurred among a group of schoolgirls who stomped upon fallen fruit. They developed a streaky, vesicular dermatitis on their legs, similar that poison ivy contact dermatitis.92

The Proteaceae family comprises 1050 species in 62 genera and is found predominantly in the tropics. The most important genus of this family is the genus Grevillea which is made up of approximately 360 species, most native of Australia, where they range from low shrubs to forest trees. A number of different Grevillea species and hybrids, specially of the eugrevillea section, appear to cause allergic contact dermatitis.94 The most important species are Grevillea robusta Cunn, also known as silky oak or silver oak and Grevillea x Robyn Gordon a natural hybrid between Grevillea banksii R. Br. and Grevillea bipinnatifida R. Br. which is perhaps the most important plant in this genus from human health perspective and probably represent the most common cause of plant-induced dermatitis in Australia.95

The allergens appear to be different between the species and among their hybrids. The allergens of G. robusta are 5-tridecylresorcinol (grevillol), 5-pentadecylresorcinol and 5-pentadecenylyresorcinol. Grevillea banksii R. Br. shows the resorcinol derivative pentadecylresorcinol. Others long carbon chain alkenyl resorcinol are also the haptens in Grevillea Robyn Gordon.96

Contact with the wild and cultivated tree, especially with the flowers, as well as with objects made with its wood, induces a bullous eruption similar to that caused by poison ivy and poison oak (Toxicodendron spp.).97 Grevillea poisoning was described among men who cut the fallen trees and developed a severe bullous contact reaction.98

Primulaceae is a wide family of flowering plants with about 1000 species in 24 genera. Despite its large number of specimens and cosmopolitan distribution only Primula spp. presents a common dermatological hazard. Primula was exported from China to England in the year 1880. Their beautiful flowers, long flowering period and their ease of care, helped a quick introduction into Europe, with less success in America. For a number of years Primula obconica Hanse was the most common cause of plant-induced contact dermatitis in Europe, however since the introduction of primin-free P. obconica Hanse into the European market, its incidence has declined.99 Other species of Primula are reported to be allergenic, such as P. auricula L., P. denticulata Sm. and P. vulgaris Huds, and vary widely in their allergen content.100–102

The primin (2-methoxy-6-n-pentyl-p-benzoquinone) is the major allergen of primrose dermatitis, a quinone formed by oxidation of its biosynthetic precursor miconidin (Fig. 8), however other allergens such as primetin (a flavone),103 and miconidin (2-methoxy-6-pentyl-1,4-dihydroxybenzene)104 has also been suggested. Primin is contained in the terminal cells of the microscopic glandular hairs on the surface of the leaves, stems and flowers. The allergen content of the plant varies considerably, depending on season, the number hours of sunshine, the method of cultivation, and the horticultural variety, which explains the striking seasonal variation in its allergenicity, being greatest in the summer and lower in winter months.

Figure 8.

Chemical structures of primin and miconodin.

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Sensitization to P. obconica Hance can occur by direct contact with plants or by indirect contact, e.g. via hand-shakes, door handgrips or paper fibers. Primin can be released through pollen or small dust particles, causing an air-borne allergic contact dermatitis in some sensitized patients.105

Dermatitis most commonly occurs in elderly women and a variety of cutaneous reactions have been described: Facial dermatitis, alone or combined with limb dermatitis and hand dermatitis.42,106,107 Eruptions vary from linear to erythematous papules, vesicles and bullae, and to erythema-multiforme and lichen planus like lesions.108–113 Few cases of airborne dermatitis and111,114,115 facial eruption mimicking herpes simplex116 as well as one case presenting as vitiligo117 have also been reported.

In order to reduce the incidence of allergic primin contact dermatitis, a primin-free Primula obconica Hance was developed.118 Although its introduction reduced significantly the cases of among cultivars, it still remains as an important contact allergen, justifying its maintenance in the standard series.

This family includes 900 species in 150 genera which are found in tropical and temperate regions especially in southern Africa and Australia. Is an important cause of phototoxic reactions although some cases of ACD of the citrus genus have also been reported.

Twelve species are native to southern China, south-east Asia and Indo-Malaysia; however, with the aim of achieving greater fruits, with more juice, better taste and lack of seeds, numerous other species have emerged from various artificial crosses. The most common species are Citrus sinensis L. (orange), Citrus aurantium L. (Bergamot) and Citrus Limon L. Burm. Fil. (lemon). Besides its use in the food industry, citrus used to carry out aromatic oils from the flowers and fur, used in perfumery and in the manufacture of soaps and cosmetics.

Allergic contact dermatitis to citrus fruits is unusual and hand dermatitis has been described in food handlers.119 The potential sensitizers include geraniol, citral and a the hydroperoxide derivative of d-limonene120 which are usually included in fragrances and its mechanism of sensitization is nowadays a source of research.

The Brassicacea family contains about 3200 species in 375 genera. It includes several important vegetables, such as cabbage (Brassica oleracea L.), cauliflower (B. oleracea L. v botrytis), radish (Raphanus sativus L.), horse radish (Armoracia rusticana P.Gaertn., B.Mey. & Scherb), turnip (Brassica campestris L.) and mustrard (Brassica nigra (L.) W.D.J. Koch). The Capparaceae, regarded as the tropical relative of the mustard family, comprises some 650 species of small trees and shrubs in 30 genera. The most important representative of this family is Capparis spinosa L., or caper bush, a shrub with grayish oval leaves and showy white-pink flowers with several prominent stamens that is better known for the edible bud and fruit which are usually consumed pickled.

Several species contain thioglucosides, which are broken down enzymatically, in the presence of water, to isothiocyanates, potent irritants, which appear to be also the most important allergens. Contact dermatitis from these plants can be both irritant and allergic,136,137 being its potential irritancy capacity high and its allergic contact dermatitis rare.

Allergic contact dermatitis is more commonly seen in food handlers. Raphanus sativus L. induced an acute vesiculo-bullous dermatitis of both palms in a waitress who chopped them.135 Cabbages provoked occupational contact dermatitis138 and cabbage juice can produce positive patch test reactions in patients with hand dermatitis suspected to have been caused by vegetables.139Brassica nigra induced an allergic contact dermatitis due to mustard powder in a salad maker137 and Brassica oleracea v. Botrytis (cauliflower) induced a hand eczema in a plant grower.140Capparis spinosa L. induced an acute vesiculo-bullous allergic contact dermatitis in a woman who applied a wet compress of the minced leaves and fruits to her arm.141

Patch test: Isothiocyanates present in these plants are usually primary irritants, and they can be tested at a concentration of 0.05% in petrolatum. As the irritancy of mustard oil tends to overshadow its allergic potential, positive patch test with mustard can be difficult to interpret.135

The polyacetylenes are a group of chemically reactive and biologically active compounds with a carbon-carbon triple bond or alkynyl functional group. They can be found in seven families of plants, and the majority has been isolated from the closely related plant families Araliaceae and Apiaceae. The polyacetylenic derivatives of the Araliaceae and Apiaceae are mostly the aliphatic C17-polyacetylenes of the falcarinol-type, derived from oleic acid.142 They act as very reactive alkylating agents towards, for example, thiol groups in proteins, forming hapten-protein complexes (antigens).142,143

This family of some 700 species in 55 genera consists mostly of trees and shrubs, but includes some twiners. Most species occur in tropical regions, particularly in Indo-Malaysia and tropical America. Other species are native to temperate regions, and some species have become widely distributed by horticulture and as houseplants.

Perhaps the best known temperate specie is Hedera helix L., the common ivy. The plants are native to Europe, North Africa, and Asia but are now grown in many other countries. Three main subspecies are found in Europe, namely helix (English ivy), canariensis (Canary Island ivy) and poetarum. They are a family of evergreen climbing plants usually found scrambling over rocks an through hedges or climbing up trees or walls (Fig. 12).

Figure 12.

Hedera helix.

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Falcarinol (heptadeca-1,9-diene-4,6-diyne-3-ol) and didehydrofalcarinol are the most important allergens. They are detected in stalks, leaves, and roots and may cause both irritant and allergic contact dermatitis. Falcarinol seems to be the stronger sensitizer and concentration and the ratio didehydrofalcarinol: falcarinol seems to varied considerably, depending on climate and other conditions of growth.144

Sensitization can occur through contact with plants to climb trees covered by them or by pruning or handling the plants in an occupational setting. Any site in contact with the plant may be affected and dermatitis commonly begins with an itching and erythema that in a few days develops into a vesicular eczema (Fig. 13).145 The most frequently affected sites are hands and forearms followed by involvement of the face and neck, however, involvement of trunk and legs as well as widespread dermatitis has also been reported.145,146 Urticarial-like dermatitis have also been reported.147 Immediate, possibly allergic, reactions from common ivy causing rhinitis and asthma have rarely been reported, The majority of mucosal symptoms in gardeners are probably irritant, perhaps caused by hederin.148–150

Figure 13.

Symmetrical erythematous patches after contact with Hedera helix.

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Also known as the Umbelliferae, this family of 2850 species in 275 genera is of cosmopolitan distribution but is found mainly in north temperate regions. Most of the species of dermatological importance are similar in floral structure with cluster of flowers on stalks of roughly equal length arising from a single point as an umbrella structure. Most of the members of this family have been shown to be rich in psoralenes and therefore produced phototoxic reactions. Some ornamental plants and weeds as well as edible plants of this family have also been related to allergic contact dermatitis. Two important species in dermatology are Centella asiatica and Daucus carota vars.