Auckland Allergy & Eczema Clinic

Plant Dermatitis (Phytodermatitis)

Plant Dermatitis (Phytodermatitis)

Article written: October 2002

There are thousands of plant species that can produce skin reactions. Plants can produce several types of skin reaction including:

Allergic Contact Dermatitis (ACD) due to plants

This is the phytodermatitis causing the most trouble.

In the case of a florist, gardener, or forester thinking of the possibility of plant ACD is quite easy, but for the housewife reacting to indoor plants like primula (primrose) this diagnosis is often overlooked. Factors making plant dermatitis likely include:

  • Exposed skin affected
  • Spring/summer flare
  • Hand or facial dermatitis
  • Occupational or hobby-related exposure to plants.

Plants causing Allergic contact dermatitis

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Specific Plants causing Contact Dermatitis

Alstromeria species (Inca lily & Peruvian Lily)

This is a popular cut flower that is often used by florists. It has a distinct lily-like flower set on a slender, leafy stem. ACD to alstromeria is mainly seen in florists, who have repeated contact with the flower. It typically causes chronic, fissured, dermatitis of the fingers. The fingertips are typically tender, red, fissured, and thickened and mimic the appearance of "tulip fingers", the rash seen in tulip workers. The rash may spread to involve the forearms and face. The dermatitis is sometimes associated with a loss of skin pigmentation. Tulip bulbs and alstromeria share the same allergen, Tuliposide A, and therefore patients tend to be allergic to both.


Tulips are popular spring flowers, even though they are short-lived and non-scented. ACD to tulips is predominantly seen in the flower bulb industry. ACD to tulip bulb is known as "tulip fingers", and is due to extensive contact with tulip bulb during digging, peeling, sorting and packaging. 56% of workers in an American bulb distributor were sensitised to tulips.

Chrysanthemum and other Compositae (Asteraceae)

There are about 500 varieties of chrysanthemums. These are one of the most common causes of ACD in florists. They belong to the family Compositae, also know as Asteraceae. Compositae is one of the largest plant families, containing about 20,000 species. They are generally herbaceous plants. A large number of compositae are weeds, and some are ornamentals. A few are cultivated as vegetables. The best known compositae, causing ACD, apart from chrysanthemum, are ragweed and feverfew (parthenium species).

Well known species of compositae family includes:

  • Artichoke
  • Chamomile
  • Chicory
  • Chrysanthemum
  • Daisy
  • Dahli
  • Dandelion
  • Endive
  • Feverfew
  • Lettuce
  • Marigold
  • Pyrethrum
  • Ragweed
  • Sagebrush
  • Sunflower
  • Tarragon
  • Thistle

The allergens in the Compositae family are sesquiterpene lactones. Over 100 of the identified sesquiterpene lactones are potentially allergic. Unfortunately no single sesquiterpene lactone can test for sensitivity to chrysanthemums. The patient has to be tested to the actual plant to which he/she was exposed.

Sesquiterpene lactone-induced dermatitis commonly causes a chronic, red, diffuse thickened eruption of the exposed skin, resembling a photodermatitis. The fingers or hands are often the initial site of involvement among florists and growers of chrysanthemums.

The standard Patch Test tray done at the Auckland Allergy Clinic has a screening sesquiterpene lactone mix. If this test is negative a patch test to the actual suspected plant is done.

Primrose (Primula)

Primula is an indoor plant, which is appealing because of its beautiful flowers and long flowering season. ACD due to primula is often over looked. In Europe about 50% of the relevant positive patch test reactions are clinically unsuspected. It is very rare to see the typical linear streaks of acute ACD. More commonly a nondescript rash involving the hands, face, and neck occurs. Characteristically the fingertips are affected as a result of picking off the dead flowers and leaves. . "Any housewife with dermatitis affecting the hands, arms, neck or face, should be asked about primula house plants". In our practice primin is included in the standard battery of Patch Test.

Other Plants and flowers causing contact dermatitis in New Zealand


Dermatitis can occur if crushed leaves come in contact with the skin of a sensitised person. Patch testing will confirm the diagnosis

Castor Bean

Dermatitis can occur if the juice of the leaves or stems of the plants or beans touches the skin.


These flowers can cause an itchy rash on the face, hands and forearms. This is more common in florists or gardeners.


Dermatitis can occur on the hands or arms usually when the leaves are plucked.

Rhus Dermatitis

Poison ivy and oak are members of the Anacardiaceae family of plants. These are also referred to as Rhus trees (Toxicodendron succadaneum). This plant family includes poison ivy, poison oak, and poison sumac. Poison ivy has three leaves growing out from one node on the stem. The sumac is well known for its bright orange coloured leaves in autumn. The rash from all three plants looks the same.

Anacardiaceae Family

Toxidendron Genus

  • Poison Ivy (climbing and non-climbing)
  • Poison oak
  • Poison sumac

Other members

  • Cashew: Anacardium occidentale
  • Mango: Mangifera idica
  • Ginko : Ginko bilboa
  • Japanese lacquer: Rhus vernicifera
  • Indian marking nut: Semecarpus anacardium

Individuals who are sensitive to poison ivy and oak can also develop allergic contact dermatitis to other plants in the Anacardiaceae family.

Often patients develop lines of small blisters, with sharp margins, and geographic outlines on the skin where the plant brushed against them.

Poison ivy rash is the classic example of an allergic contact dermatitis. It is a delayed type hypersensitivity, which means the rash usually develops within 12 to 48 hours vs. within 15 – 20 minutes for an Immediate Type Hypersensitivity reaction. It is not unusual for new areas of dermatitis to develop for several days after the initial outbreak.

The rash is due to skin contact with oil called urushiol. Urushiol is composed of a mixture of catechol and is found in the sap of any cut or crushed part of the plant, including the leaves, stem or root. Urushiol is absorbed very quickly into the skin; therefore it is necessary to wash with soap and water within 5 to 10 minutes after exposure to prevent dermatitis.

There are 3 ways in which poison ivy sap can cause a rash:

  • Direct contact – skin touching the cut plant. This produces the well-known linear blistery rash.
  • Indirect contact – touching something which was in direct contact with urushiol. For example the fur of animals or garden tools can have tho oil stuck onto it.
  • Airborne urushiol – from burning plants making contact with the skin

About 85% of all people will develop an allergic reaction if adequately exposed to poison ivy. After adulthood there is a 50% chance of becoming sensitised if the individual wasn't before.

The rash can affect almost any part of the body, especially where the skin is thin, such as the face. Because urushiol is more slowly absorbed on thicker skin, like the palms, forearms & trunk, the rash will break out in these areas after the face. But the rash doesn't spread. Blisters and a severe itch or burning sensation often follows redness and swelling.

Diagnosis of Plant Contact Dermatitis

  • Probably the most important part of making a diagnosis of phytodermatitis is to think of the possibility.
  • Identify the plant. This should be done before trying to do any tests (including Patch Test), so that known irritant plants can be avoided. One might have to seek the help of the local Botany Department.
  • The Patch Test is the only sure way of confirming an allergic contact dermatitis. Patch test can be done with the following:

1. Fresh Plant: leaf, stem, petal, seed, root, bulb
2. Fresh sawdust in 10% petrolatum
3. Commercial plant allergen if available

There is a possibility of sensitising to a strong chemical by patch testing. It is for this reason why poison ivy is not usually patch tested. For plants with unknown irritancy it might be necessary to patch test 10 normal subjects, to act as controls. If there is a delay before plant can be patch tested it should be kept frozen.

Plants causing Photodermatitis (Phytophotodermatitis)

Compounds related to furocouramins (psoralens) usually cause photosensitization(contact dermatitis due to plants). Two requisites for initiation of phytophotodermatitis are contact with a sensitising plant (furocouramin) and exposure to ultraviolet light ( wavelength greater than 320 nm), usually sunlight. Therefore, this dermatitis is usually seasonal.

Phytophotodermatitis produces erythema and blisters on first exposure followed by persistent hyperpigmentation (darkening of the skin). This darkening of the skin can persist for months. The mechanism of this rash is phototoxic, compared to poison ivy, which is contacted allergic. This rash also causes a burning pain, compared to the itching caused by poison ivy.

Common plants causing Phytophotodermatitis


Plants causing Contact Urticaria

Contact urticaria usually occurs within 15 minutes of the plant coming in contact with the skin. This is an example of immediate (Type 1 hypersensitivity) vs the delayed (Type IV hypersensitivity) seen in allergic contact dermatitis.

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