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Phytophotodermatitis Workup

  • Author: William P Baugh, MD; Chief Editor: William D James, MD  more...
Updated: Jul 24, 2014

Laboratory Studies

See the list below:

  • Phytophotodermatitis (PPD) is a clinical diagnosis. All laboratory data obtained are used to support the diagnosis and to exclude other diseases in the differential diagnosis.
  • Serum psoralen levels may be checked if unknown ingestion of psoralens is suspected.
  • Porphyrin levels may be obtained to rule out porphyria cutanea tarda.
  • If the clinical picture does not clearly distinguish between photoallergic and phototoxic dermatitis, performing a photopatch test may be prudent. The photopatch test should include testing for sunscreens because they may be a cause of allergic contact dermatitis associated with sun exposure.


See the list below:

  • A skin biopsy may be performed to determine the clinical diagnosis if it remains in question and to help distinguish between allergic contact, photoallergic, and photodrug reactions.

Histologic Findings

Classic histopathologic features of phytophotodermatitis include the following:

Epidermal hyperkeratosis, with or without parakeratosis, is observed. Scattered necrotic keratinocytes (apoptotic cells) are found in the epidermis. Sunburn cells (cells with pyknotic nuclei, increased volume, and pale staining cytoplasm) are also found in the epidermis. Slight spongiosis is observed in the epidermis. Minimal inflammatory cell infiltrate consisting of neutrophils (predominant cell type early on), lymphocytes (less common), and macrophages and melanophages (late) is present. Subepidermal blistering and extravasation of erythrocytes may or may not be present. Pigment incontinence with melanophages is observed in the papillary dermis. The dermis shows some edema and enlargement of vascular endothelial cells.

Both light microscopy and transmission electron microscopy in animal models show keratinocyte necrosis and vacuolization within 24 hours. Within 72 hours, intraepidermal and subepidermal blistering is visible.[19, 20]

Contributor Information and Disclosures

William P Baugh, MD Assistant Clinical Professor of Dermatology, Western University of Health Sciences; Medical Director, Full Spectrum Dermatology; Consulting Staff, Department of Dermatology, St Jude Medical Center

William P Baugh, MD is a member of the following medical societies: American Academy of Dermatology, American Society for Laser Medicine and Surgery, Christian Medical and Dental Associations

Disclosure: Nothing to disclose.


David Barnette, Jr, MD Voluntary Associate Clinical Professor, University of California San Diego School of Medicine

David Barnette, Jr, MD is a member of the following medical societies: American Academy of Dermatology, American Society of Dermatopathology

Disclosure: Nothing to disclose.

Walter D Kucaba, DO Private Family Practice, Simpsonville, South Carolina

Walter D Kucaba, DO is a member of the following medical societies: Aerospace Medical Association, American Medical Association, American Osteopathic Association, Undersea and Hyperbaric Medical Society

Disclosure: Nothing to disclose.

Cynthia L Chen, DO, DO Intern, Pacific Hospital of Long Beach, California

Cynthia L Chen, DO, DO is a member of the following medical societies: American Osteopathic Association, California Medical Association, American Osteopathic College of Dermatology, Los Angeles County Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

Richard P Vinson, MD Assistant Clinical Professor, Department of Dermatology, Texas Tech University Health Sciences Center, Paul L Foster School of Medicine; Consulting Staff, Mountain View Dermatology, PA

Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Texas Medical Association, Association of Military Dermatologists, Texas Dermatological Society

Disclosure: Nothing to disclose.

Jeffrey J Miller, MD Associate Professor of Dermatology, Pennsylvania State University College of Medicine; Staff Dermatologist, Pennsylvania State Milton S Hershey Medical Center

Jeffrey J Miller, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, Society for Investigative Dermatology, Association of Professors of Dermatology, North American Hair Research Society

Disclosure: Nothing to disclose.

Chief Editor

William D James, MD Paul R Gross Professor of Dermatology, Vice-Chairman, Residency Program Director, Department of Dermatology, University of Pennsylvania School of Medicine

William D James, MD is a member of the following medical societies: American Academy of Dermatology, Society for Investigative Dermatology

Disclosure: Nothing to disclose.

Additional Contributors

Craig A Elmets, MD Professor and Chair, Department of Dermatology, Director, Chemoprevention Program Director, Comprehensive Cancer Center, UAB Skin Diseases Research Center, University of Alabama at Birmingham School of Medicine

Craig A Elmets, MD is a member of the following medical societies: American Academy of Dermatology, American Association of Immunologists, American College of Physicians, American Federation for Medical Research, Society for Investigative Dermatology

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: University of Alabama at Birmingham; University of Alabama Health Services Foundation<br/>Serve(d) as a speaker or a member of a speakers bureau for: Ferndale Laboratories<br/>Received research grant from: NIH, Veterans Administration, California Grape Assn<br/>Received consulting fee from Astellas for review panel membership; Received salary from Massachusetts Medical Society for employment; Received salary from UpToDate for employment. for: Astellas.

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A 37-year-old white woman presented to the clinic complaining of a rash on the medial part of her right thigh and left arm that was acquired after clearing some weeds in her yard. A phototoxic combination of sunlight and a psoralen-containing plant produced this bizarre linear vesicular eruption.
Closer clinical view of bizarre angulated vesicular streaks, which occurred after contact with a plant and ultraviolet light exposure.
A 26-year-old female airline flight attendant exposed to lime while serving drinks en route to the Caribbean. During the Caribbean layover, she had significant sun exposure. The combination of lime juice and sun exposure led to a drip-pattern blister formation on the dorsal forearm consistent with phytophotodermatitis. This picture clearly delineates the potential severity of phytophotodermatitis with extensive blister formation.
The 2-month follow-up picture of a patient with a drip-pattern blister formation on the dorsal forearm demonstrates the potential postinflammatory pigmentation changes and scarring that may occur with severe blistering of phytophotodermatitis.
Close-up view of vesicular linear streaks with morphology suggestive of scattered foci of epidermal necrosis.
Queen Anne's lace, a member of the Umbelliferae family of plants, is well known to produce a furocoumarin-induced phototoxic eruption.
Ficus. The common fig contains furocoumarins and should be considered amidst the list of potential offending agents that cause phytophotodermatitis.
Table. Common Causes of Phytophotodermatitis
Family Genus Species Common Names Main Compounds
Umbelliferae Amni majus Queen Anne's lace, Bishop's weed 8-methoxypsoralen (8-MOP), 5-methoxypsoralen (5-MOP), imperatorin
Heracleum sphondylium Cow parsnip 8-MOP, 5-MOP, imperatorin, phellopterin
Heracleum mantegazzianum Giant hogweed, Cartwheel flower 8-MOP, 5-MOP, imperatorin, phellopterin
Pastinaca sativa Parsnip 8-MOP, 5-MOP, imperatorin, isopimpinellin
Apium graveolens Celery Psoralens, 8-MOP, 5-MOP
Rutaceae Citrus bergamia Bergamot lime 5-MOP
Citrus maxima Zabon[10] 5-MOP
Dictamnus albus Gas plant, “Burning bush of Moses” 8-MOP, 5-MOP
Moracea Ficus carica Fig Psoralens, 5-MOP
Leguminosae Psoralea corylifolia Bavchi, Scurf pea Psoralens
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