No, this tongue-twisting mouthful is not a rash caused by taking photographs of Fido – or do you say “Phyto?” Like so many terms in medicine and, particularly, in dermatology, a clearer understanding of what we’re talking about can be gleaned by breaking up the term into parts. In this case the term “Phytophotodermatitis” can be broken into 4 words, all of them Greek in origin – 1) phyto; 2) photo; 3) derma; and 4) itis. The word, “phyto,” is Greek for plant. The word, “photo,” also Greek, means light, in this case sunlight. “Derma,” obviously, means skin, and “itis” means inflammation, again both Greek terms. Put together and you have it: a plant – sunlight – skin – inflammation, or, in other words, an inflammation of the skin caused by plants and sunlight: phytophotodermatitis. One may ask why the “t” is placed between “derma” and “itis,” to spell the word “dermatitis” and not “dermaitis?” It is likely only for greater ease in pronunciation and nothing more.

One can develop a rash caused by plants alone and one can also develop a rash caused by the sun alone. A perfect example of a rash, or dermatitis, caused by a plant alone is poison ivy in individuals who are sensitive to urushiol or rhus, the chemical in poison ivy that is responsible for the skin reaction. There are also rashes, significantly less common than poison ivy, which are caused by exposures to sunlight alone. However, in this case, both elements, i.e. exposure of the skin to both the plant and to the sun, must be present for the reaction to occur. In other words, exposure to the plant alone will not cause the rash AND exposure to the sun alone will also not cause the rash.

There are several plants which can cause this type of reaction and each of these have a similar chemical or related group of chemicals, generically known as furocoumarins (or furanocoumarins), within them, which are responsible for the rash when the skin is exposed to the sun. Typically, with exposure to the plant followed by exposure of the area of skin on which these chemicals are deposited to the sun, a red, burning or stinging, red and sometimes blistering rash develops within 24 – 48 hours after these exposures. However, this reaction is transient, disappearing totally, only to reappear a day or two as a darker brown color. Burning, rather than itching, also helps to distinguish a phytophotodermatitis from the allergic contact dermatitis of poison ivy and its rhus relatives, poison sumac and oak.

So what types of plants do you and I need to look out for or avoid in order to prevent getting phytophotodermatitis? The following provides a comprehensive list of the most common plants which cause this problem. It is not, however, an exhaustive list. Again, remember that these plants alone will not cause a rash (unless, of course, one has an allergy to a specific plant). Exposure of the skin to the plant followed by sun exposure or other ultraviolet exposures, i.e. tanning beds, are both necessary.

Common Plant Name, Identification and Exposure

• Parsnips (Pastinaca Sativa)
Identification: Pale orange to yellow color taproot vegetable with green, above-ground leaves (similar to carrots)
Exposure: Gardners, restaurant workers, grocers, household

• Parsley (Petroselinum Hortense and Petroselinum Crispum)
Identification: Numerous, bright-green, 1/4 –1 in., flat, pointed leaves in bunches of 3, with a pale taproot smaller than carrots
Exposure: Gardners, restaurant workers, grocers, household. Note: there are different varieties of parsley and the scientific nomenclature is both confusing and inconsistent between various sources

• Carrots (Daucus Carota)
Identification: Well-known orange taproot vegetable with green, above-ground leaves
Exposure: Gardners, restaurant workers, grocers, household

• Celery (Apium Graveolans) both the vegetable and the seeds
Identification: Another well-known vegetable, having long, pale-green, ribbed stalks, with several green, pinnate (feather-like) leaves on their ends; multiple stalks found in parallel bunches
Exposure: Gardners, restaurant workers, bartenders, grocers, household

• Coriander (Coriandrum Sativum) also commonly known as Cilantro; less commonly as Chinese Parsley or Dhania
Identification: Green, thin-stalked, herbal plant, up to 20 in. in height, with variably-shaped, either broadly lobed or slender and feathery, green leaves
Exposure: Gardners, restaurant workers, household

• Fennel (Foeniculum vulgare) including Florence Fennel or Finocchio, both the whole herb and the seed
Identification: Bluish-green, thin-stemmed herbal plant, up to about 7 ft. in height, with thin, threadlike leaves and tiny, yellow flowers on the ends of 20–50 short, thinner stalks forming 2–6 in. wide, umbrella-like structures on the ends of its stems; thin, grooved, brown-green, 1/8–1/4 in. long seeds
Exposure: Gardners, restaurant workers, household

• Anise (Pimpinella Anisum) also known as Aniseed
Identification: Green, thin-stemmed plant, up to 3 ft. in height, with 1/2 to 2 in. long, fanlike leaves at base of plant, and more numerous feathery and thinly divided leaves higher on the stems, and with numerous, white, 1/8 in. diameter on the ends of thinner stalks forming umbrella-like structures; multilobed (7–8), star-shaped orange-brown fruit, each lobe containing a single 1/8–1/4 in. long seed.
Exposure: Gardners, restaurant workers, household

• Dill (Anethum Graveolens)
Identification: Herb similar in appearance to Fennel and Anise but with smaller umbrella-like flower bearing structures
Exposure: Gardners, restaurant workers, grocers, household

• Fig (Ficus Carica)
Identification: Well-known, edible 1/2–2 in. long, green to brown, fleshy fruit, which grows on a 19–33 ft. deciduous tree, with smooth, gray bark and 5–10 in. long by 4–7 in. wide, deeply- lobed, green leaves
Exposure: Fruit pickers, grocers, household

• Lemon (Citrus x Limon) and Lime (Citrus Aurantifolia)
Identification: Well-known yellow and green rind citrus fruits
Exposure: Restaurant workers, bartenders, household

• Giant Hogweed (Heracleum Mantegazzianum) also commonly referred to as Wild Parsnip
Identification: Located in northeastern and northwestern U.S. as well as central and eastern Canada. Giant Hogweed is considered a noxious weed. Tall (6–23 ft.), stout (1–4 in. diameter), reddish-purple, ridged and branched stems, with centrally-haired, raised nodules and leaf stalks, with course, white hairs at their bases and large (3–6 ft. wide) deeply cut, compound leaves. Mature plants produce numerous white flowers clustered in an umbrella-shaped flat-topped head that is up to 31 in. in diameter
Exposure: Hikers/groundskeepers - so-called “strimmers” or “weed eaters” dermatitis; especially along riverbanks. Note: This plant is particularly dangerous, causing severe reactions, sometimes requiring hospitalization. Eye exposures can lead to temporary or permanent blindness.

• Cow Parsnip (Heracleum Spondylium) also commonly referred to as Hogweed and Indian Celery
Identification: Located throughout continental U.S. except Golf coast and a few neighboring states. Cow Parsnip is nearly identical to Giant Hogweed except shorter, reaching a maximum height of about 6 ft., and other features proportionately smaller
Exposure: Hikers, groundskeepers - “strimmers” or “weed eaters” dermatitis

• Bushrue (Cneoridium Dumosum) also referred to as Coast Spice Bush
Identification: Located throughout southern and Baja California. Bushrue is short (2–4 or 5 ft.), highly-branched, spicy-smelling shrub covered with small, narrow, shiny, green leaves, with clusters of small, 4–5 pettled, white flowers, appearing after winter rains, followed by 1/4 in., reddish-green berries
Exposure: Gardners, landscapers, hikers

• Western water hemlock (Cicuta Douglasii) also known as Douglas water hemlock;

Northern water hemlock (Cicuta Virosa) also known as Mackenzie’s water hemlock and Cowbane;

Spotted water hemlock (Cicuta Maculata) also known as Spotted parsley and Spotted cowbane;

Bulbous water hemlock (Cicuta Bulbifera) also known as Bulblet-bearing water hemlock;

   Poison hemlock (Conium Maculatum)
Identification: All 5 of these have similar characteristics: Native to North America and Europe. Perennial, green herbaceous plants, which grow up to 8 ft. tall, with distinctive small green or white flowers arranged in an umbrella shape. Seen along streams and ponds, in marshes, swamps and wet meadows.
Exposure: Hikers, hunters, fishermen.       NOTE: Although phytophotodermatitis can be seen with these plants, they are more noteworthy because they are highly poisonous if ingested. Water hemlocks produce central nervous system stimulatory effects, including seizures and, potentially, death. Poison hemlock produces neurotoxic effects resulting in ascending muscular paralysis, eventual paralysis of the respiratory muscles, and death.

Treatment of the acute phase of phytophotodermatitis is all that is required and is brief. The dermatitis is a self-limited process, lasting for only 2 – 3 days. Cold, wet compresses help to reduce stinging or burning and might reduce any blistering. Topical steroid creams, lotions, gels or sprays may also be helpful, but these should be of sufficient strength, which can only be gotten by prescription. Nonsteroidal anti-inflammatory drugs (NSAIDS) like ibuprofen should also help the inflammation. Oral steroids like prednisone are seldom required. Unfortunately, the dark pigmentation which results from the reaction may take many months to resolve and treatment is difficult but unnecessary. Once again, avoidance of the offending plant or plant product and the judicious daily use of sunscreen, one specifically blocking UV-A, are paramount for prevention.