University of Vermont Extension
Department of Plant and Soil Science
Summer News
Article
SOME PLANTS AND SUN DON’T MIX
Dr. Leonard Perry, Extension
Professor
University of Vermont
If you’re a gardener or merely
enjoy being outdoors, you may have heard if not learned first hand of the skin
reactions caused by some plants—dermatitis.
Common examples are rashes from the oil of poison ivy or brushing the
leaves of stinging nettles. Also common,
but often overlooked and misdiagnosed, are the rashes caused by exposure to
certain plants in sunlight. Some common
culprits are garden plants such as gas plant, wildflowers such as Queen Anne’s
Lace, vegetables such as celery, and one of the most common—limes.
These “phytophotodermititis” skin
rashes (dermatitis) are caused by the reaction of the plant (phyto) toxic
chemicals (“furocoumarins”), combined with the UV rays from the sun
(photo). While not all people get these
reactions, they are possible in anyone if high enough concentrations under the
right conditions. Agricultural workers
and gardeners, bartenders (on beaches and outside), and children (from running
through wild growth areas) are some of the populations in which this problem is
often seen.
If going to the beach on
vacation, or merely partying on a sunny patio, beware of popular drinks with citrus
wedges and juice, particularly limes (the problem is more the juice from the
rinds than from the pulp). A beer
commercial that appears humorous on the screen may cause dire problems in
reality. In the scene, a woman squirts
lime juice on her boyfriend for looking at a gorgeous girl. Does she know she
may be causing phytophotodermititis (sometimes called “margarita dermatitis” or
“lime disease”), resulting in a rash on his face? Others have reactions from
using lime juice remedies as insect repellents.
Rashes and lesions begin about a
day after exposure, often burning and may blister. While they peak in 2 to 3 days, the
pigmentation may last for weeks or months.
The more fortunate only get the pigmentation without the burning and
blistering. Exposure is more common in mid
to late summer when the amount of chemical is highest in offending plants, skin
exposure to sunlight is greatest, skin is wet from swimming or sweating, and
lime drinks are more common outdoors.
Symptoms of photodermititis are
different from those of poison ivy and other plants in that they cause burning
not itching, are only in areas exposed to sunlight, are often in random linear
streaks or patterns (such as from lime juice running down skin or brushing
against plants), and develop pigmentation.
Such pigmented areas may be sensitive to UV light for several
years. Getting the toxic substance on
hands and then touching skin (as parents grabbing children), can lead to
fingerprint patterns. Offending weed parts
thrown against skin, as with weed trimmers, can cause a buckshot appearance to
the rash.
There are three main plant families that cause this disease. The carrot family, Umbelliferae or Apiaceae,
is the most common in gardens and natural areas. The false Queen Anne’s lace or bishop’s flower
(Ammi majus) has a flower similar to
Queen Anne’s lace (Daucus carota),
only is annual not biennial as the latter.
The former was used as early as 2000 BCE for the treatment of certain
diseases, but the cause of this plant and sun reaction was not discovered until
the 1930’s. Queen Anne’s lace is the
common roadside wildflower, is useful to attract beneficial insects and
pollinators, is the relative of our cultivated carrot, and yet can cause such
reactions. The false Queen Anne’s lace is often used in flower arranging.
Other members of the carrot
family growing wild that can cause problems are the closely related
cow parsley, cow parsnip, and the invasive giant hogweed. These have white flowers compared to the wild
parsnip with yellow flowers, the latter escaped from cultivation and also
becoming invasive in many regions. Herbs
in this family to use care with include angelica (wild angelica too), parsley,
and fennel. Handling the edible crops celery
and carrot in this family, especially repeatedly by agricultural workers, can
cause problems. An interesting point
found through research is that some plants, such as celery, may develop much
higher levels of these toxic (to humans) furocoumarins in response to a disease
attack. Such substances, termed
“phytoalexins,” help plants to resist disease organisms.
The rue family, Rutaceae,
includes the tropical citrus culprits of this disease, as well as the temperate
garden plants garden rue (Ruta graveolens)
and gas plant (Dictamnus albus). The latter exudes a “gas” in the air on still
summer evenings that can be ignited briefly.
Some conjecture that this may have been the burning bush that Moses saw
on Mount Sinai.
The last main family of
significance with this disease is the mulberry, Moraceae, the main culprit
being the fig tree (Ficus carica). Similar to the citrus, symptoms arise from
getting the juice on the skin (leaving it on lips can be a problem) rather than
from eating the fruit. Pruning figs,
harvesting, even using homemade fig decoctions as tanning lotions can cause
problems.
The first step to treatment is to
avoid such plants, or treat them with caution until you learn your
sensitivity. Wear gloves and cover skin
when working around such plants. If you
do end up with lesions, apply cool wet compresses. If lesions are extensive and quite painful,
consult a physician who may prescribe topical steroids.
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