Author: A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. September 2014.
Phytophotodermatitis is a phototoxic reaction to contact with certain plants.
Phytophotodermatitis generally occurs during in spring or summer following some outdoor activity on a sunny day during which there has been contact with one of the responsible plants.
Its name has 3 components: phyto (plant), photo (light) and dermatitis (inflammatory rash).
During the acute inflammatory stage, itchy blisters and reddened patches appear on exposed skin, usually the forearms or lower legs. These are often irregularly distributed and odd in shape. Linear lesions are characteristic. In some cases, the inflammatory phase is not observed.
After a few days the redness and blistering settles down, but is replaced by unsightly and bizarre pigmentation at the same sites. The pigmentation is more pronounced in dark skin compared to fair skin. This postinflammatory pigmentation may persist for weeks to months.
Phytophotodermatitis is induced by the action of long wavelength ultraviolet radiation (UVA) on a plant chemical called furocoumarins (psoralens) on the skin surface. Contact with the plant, fruit or vegetable may have been brief and unnoticed. The reaction depends on:
The reaction causes inflammation in the epidermis (contact dermatitis) and activation of melanocytes (pigment cells) to produce melanin pigment.
Pigmentation due to phytophotodermatitis is partly epidermal melanosis (ie pigment is within the skin cells) and partly dermal melanosis (ie the pigment is deeper in the skin).
Responsible plants include:
Berloque dermatitis is a special form of phytophotodermatitis caused by exposure to perfumes. These perfumes contain a high concentration of bergapten (5-methoxypsoralens).
Berloque dermatitis is rare nowadays, but may arise if an older fragrance is applied to the skin. Current regulations restrict the concentration of bergapten so that it is below the threshold required to cause contact dermatitis or pigmentation.
The acute inflammatory dermatitis due to berloque dermatitis is sometimes unnoticed and the patient may present with streaky pigmentation on the neck or wrist.
Photochemotherapy (PUVA) is a treatment for inflammatory skin diseases such as psoriasis and eczema. The treatment involves taking psoralens by mouth or applying psoralens solution to the skin, followed by exposure to UVA, in controlled circumstances.
PUVA has beneficial effects on the skin diseases, but as it involves the same process as occurs in phytophotodermatitis, it can result in excessive pigmentation. This can be quite noticeable after topical or bathwater PUVA.
By the time pigmentation has occurred, the inflammatory phase of phytophotodermatitis is over. This means that anti-inflammatory treatments like topical steroids are only useful in the early phase of redness and blistering.
The postinflammatory pigmentation that follows phytophotodermatitis responds poorly to treatment with bleaching creams. It fades gradually over weeks to months. Using covering clothing and broad spectrum sunscreens, affected skin should be protected from further sun exposure, which might cause the pigmentation to darken. It can be disguised using cosmetic camouflage make-up.
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