Are You Confident of the Diagnosis?

What to be alert for in the history


The most common history for those developing ICD to plants is direct exposure, often prolonged, with plants containing irritants. Often, fissuring or dermatitis will develop on fingertips/fingers as the hands are most commonly in contact. Dryness, fissures, scaling, and erythema chiefly affect the fingertips, hands, and forearms and are often accompanied by subungual hyperkeratosis.


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There are two distinct exposure methods that should be taken into account for ACD to plants. The first is the most intuitive, direct exposure to allergenic plants leading to dermatitis often in a linear distribution. The second is much less intuitive – exposure to plant extracts in topical personal care products.


The most common causes of phototoxic reactions from plants are exposures to citrus (lime, lemon and orange). This may occur when citrus is used in an outdoor setting while preparing beverages. The phototoxic furocoumarin is in the citrus juice and when exposed to sunlight causes an exaggerated sunburn-like reaction. Other causes are figs and roots/grasses in the umbilliferae family.

Characteristic findings on physical examination

Some plants have allergens or potent irritants and are able to produce a dermatitis in a linear fashion on areas exposed for short periods of time, such as brushing up against a bruised or broken leaf/stem. The most typical presentation of ACD is linear, vesicular and pruritc dermatitis on exposed areas. Extensive exposure may lead to extensive dermatitis on widespread body surface areas. The primary lesions tend to be vesicular coalescing plaques of dermatitis. Irritant exposures may present with vesiculation and erythema. With chronic exposure for either type of dermatitis, a hyperkeratotic, fissuring, erythematous dermatitis may be present. A common finding is fingertip hyperkeratosis and fissuring.

Expected results of diagnostic studies

Diagnostic studies are often not needed for irritant contact and clear allergic contact exposures, though rarely a skin biopsy may be useful. Diagnosis is confirmed by taking an appropriate history and confirmatory skin examination. It is not possible to predict which of the many potential allergens is the cause of a dermatitis from a product. In most cases, personal care products contain multiple allergens including plant extracts both as active ingredients and/or as fragrances as well as many preservatives. For allergies to plant extracts used in personal care products, diagnostic patch testing is helpful.

Who is at Risk for Developing this Disease?

Nearly everyone is at risk for developing plant dermatitis of some sort during their lifetime. In the United States, the most ubiquitous cause of allergic contact dermatitis is the Anacardiaceae family of plants (poison oak, poison ivy and sumac). Approximately 70% of individuals living in endemic areas will develop ACD to this family during their lifetime. The risk for developing poison ivy is directly related to exposure. It is most commonly seen in individuals with outdoor exposures from 2 to 7 days before developing pruritic dermatitis on exposed areas. Phytophotodermatitis occurs in those exposed to furocoumarin-containing plants and subsequent UV/sunlight exposure.

What is the Cause of the Disease?



All ICD is caused by caustic or irritant action, directly on the skin. It is not an immunologically mediated process; it is toxic only.


Oxalates: irritant crystals in the plant leaves, stems and/or roots

Furocoumarins: phototoxic chemical naturally produced. Requires sunlight for reaction.

Solanacaea: capsaicin in these plants cause stinging/burning

Onion/Garlic (Allium spp): diallyl disulfide causes both allergic and irritant reaction, often on fingertips

Brassicaceae family (including mustard and radish): thiocyanates present in all parts of the plant

Euphorbiaceae (florist’s croton and spurges): phorbol esters present in entire plant

Ranunculaceae (buttercup flowers): protoanemonin glycoside in damaged plants can produce vesiculation and linear streaks similar to phytophotodermatitis



ACD is a type IV delayed-type hypersensitivity reaction. These reactions require both an initial sensitization through epidermal exposure, Langerhans cell processing, presentation to T-cells in the regional lymph nodes thus producing memory T-cells. On subsequent re-exposure, dermatitis is produced through this Th2 dominant reaction.


The most common plant allergens/families are outlined here:

Anacardiaceae: Urushiol in this large family produces dermatitis. Common sources are poison oak/ivy. Less well known sources: cashew fruit/shells, mango skins, Japanese lacquerware made from the sap of the Japanese lacquer tree.

Compositae family: A large family of common plants. The most common cause of dermatitis is the chrysanthemums. Also includes echinacea, calendula, feverfew and chamomile.

Tulip and Peruvian Lilly (alstroemeria): common cause of hand dermatitis in florists.

Tea tree oil (Melaleuca alternifolia): Often used in “alternative” or “natural” preparations. Older, more oxidized tea tree oil is more allergenic.

Fragrances: The list of plants with potential fragrance cross-reactions is nearly endless. Common plant allergens include lavender, jasmine, rose, bergamot (also a phototoxin)

Onion/Garlic: Allergen is diallyl disulfide.

Systemic Implications and Complications

There are minimal systemic implications or complications of topical exposures to plant irritants and allergens in most cases. Ingestion of calcium oxalates can be both a bothersome or potentially life-threatening exposure. Chewing of leaves of oxalate-containing plants produces burning of the mouth and throat, choking and gagging.

Significant ingestions may lead to severe digestive upset, breathing difficulties and possibly coma and death. Permanent liver and kidney damage may also occur.

Treatment Options


  • Topical therapy is adequate for mild cases. Fluocinolone 0.5% or Triamcinolone 0.1% applied to the involved sites in appropriate amounts will speed healing.

  • Oral therapy is rarely necessary. Over-the-counter diphenhydramine 12.5 or 25mg by mouth as necessary may be used if pruritus is bothersome.


  • Topical therapy: For localized, smaller area dermatitis with significant symptoms, clobetasol 0.05% used twice daily until symptoms/dermatitis resolves or for 3 weeks. Widespread dermatitis responds to triamcinolone 0.1% cream used twice daily. When dispensed in a 454g jar this will provide adequate amounts of medication for a large surface area. Over-the-counter oatmeal baths may be soothing.

  • Oral therapy: For widespread, symptomatic dermatitis in amenable individuals, oral prednisone will alleviate symptoms and speed recovery. One tapering dosage regimen is prednisone 10 mg tabs by mouth: 6 tabs daily for 4 days, then 4 tabs daily for 4 days, then 2 tabs daily for 4 days, finally 1 tab daily for 4 days. Oral antihistamine agents are useful for sedation when sleep is desired. Hydroxyzine 12.5 to 25mg by mouth, as necessary up to 4 times daily is often helpful for symptomatic relief, predominantly due to its sedating effects. Non-sedating antihistamines are unlikely to be helpful, as these outbreaks are not histamine driven.

Topical antipruritic agents containing diphenhydramine or pramoxine are not recommended due to the risk for development of type IV allergy.

Considering the self-limited nature of these conditions, in most cases, physical modalities such as phototherapy are not necessary. For longer duration, chronic dermatitis possibly caused by plant extracts in topical products, phototherapy may be useful in clearing dermatitis after an allergen has been identified. Surgical therapy for these conditions is not necessary or desired.

Optimal Therapeutic Approach for this Disease

For all severity of dermatitis from plants, topical therapy is preferable for first-line treatment. Topical corticosteroids are safe and effective with appropriate use for self-limited dermatitides such as plant allergic contact dermatitis. For mild disease, oral therapy is rarely warranted. For most, symptomatic relief (decreased pruritus) begins within 6 hours of application of an appropriate-strength topical corticosteroid. Often, full resolution of dermatitis will take 1 to 2 weeks.

Severe, widespread and symptomatic cases may require additional oral therapy with antipruritics and corticosteroids in addition to topical therapy. Some symptomatic relief with oral corticosteroids often begins within 6 hours of the first dose. Severe dermatitis may take longer to resolve, but many cases will be clear or nearly clear within 2 weeks. Oral corticosteroids should be carefully used in those with hypertension or diabetes.

Patient Management

These conditions are self-limited in most cases. For most, as-necessary follow-up is all that is necessary. For suspected plant extract dermatitis that you are not able to figure out clinically, consider referral for patch testing.

In general, barrier creams are ineffective in the prevention of ACD. The one exception to this generality is the commercially available product to prevent poison oak/ivy dermatitis caused by urushiol – Ivy Block. In clinical studies, Ivy Block (quaternium-18 bentonite) completely prevented or significantly decreased reactions to the urushiol. Tetrix is an oil-in-water emulsion that is useful for preventing ICD. It is unclear if it is useful in preventing ACD.

Management of those exposed to plants in an occupational setting is challenging. For many, the exposures are due to repetitive use of the hands/fingers to trim and arrange flowers, such as in a florist. Use of cotton gloves alone will not prevent allergen transfer from the plant to the fingers. Latex gloves provide more protection, but the allergens are able to diffuse through latex usually within several hours. Nitrile/plastic gloves provide better protection. Unfortunately, chronic use of gloves may lead to development or worsening of ICD due to the maceration and wet/dry cycles from sweating. The most successful treatment is avoidance of the offending plants(s). The most common causes are the Compositae plants, with the chrysanthemum being the most common cause of ACD in florists. Secondarily, Peruvian lilly/alstroemeria and tulips are causes of fingertip dermatitis.

In rare cases, a widespread dermatitis in non-exposed areas may develop. For example, poison ivy dermatitis develops on the legs 1 week following an exposure while hiking. This progresses in the typical pattern. Autoeczematization is a flare of pruritic morbilliform dermatitis, often generalized, which develops in non-allergen-exposed areas. Treatment is the same as with other allergic dermatitis.

What is the Evidence?

Chemical irritant dermatitis. In: McGovern , TW, Barkley , TM. “Botanical dermatology”. (Extensive review with tables of causes of plant ICD.)

Phytophotodermatitis. In: McGovern , TW, Barkley , TM. “Botanical dermatology”. (Extensive review of phytophotodermatitis.)

Allergic contact dermatitis. In: McGovern , TW, Barkley , TM. “Botanical dermatology”. (Broad, well written review of plants causing ACD.)

Marks , JG, Fowler , JFF, Sherertz , EF, Rietschel , RL. “Prevention of poison ivy and poison oak allergic contact dermatitis by quaternium-18”. J Am Acad Dermatol . vol. 33. 1995. pp. 212-6. (Study discussing effectiveness of quaternium-18 bentonite barrier cream.)

Schalock , PC, Zug , KA. “Protection from occupational allergens”. Curr Probl Dermatol . vol. 34. 2007. pp. 58-75. (Extensive review of barrier creams for preventing ACD.)