Plant Parts and Nomenclature
Ficus carica (common fig) is a deciduous shrub or small tree with smooth gray bark that can grow up to 10 m in height (Figure 1). It is characterized by many spreading branches, but the trunk rarely grows beyond a diameter of 7 in. Its hairy leaves are coarse on the upper side and soft underneath with 3 to 7 deep lobes that can extend up to 25 cm in length or width; the leaves grow individually, alternating along the sides of the branches. Fig trees often can be seen adorning yards, gardens, and parks, especially in tropical and subtropical climates. Ficus carica should not be confused with Ficus benjamina (weeping fig), a common ornamental tree that also is used to provide shade in hot climates, though both can cause phototoxic skin eruptions.
FIGURE 1. <i>Ficus carica</i> (common fig).
The common fig tree originated in the Mediterranean and western Asia1 and has been cultivated by humans since the second and third millennia bc for its fruit, which commonly is used to sweeten cookies, cakes, and jams.2 Figs are the most commonly mentioned food plant in the Bible, with at least 56 references in the Old and New Testaments.3 The “fruit” technically is a syconium—a hollow fleshy receptacle with a small opening at the apex partly closed by small scales. It can be obovoid, turbinate, or pear shaped; can be 1 to 4 inches long; and can vary in color from yellowish green to coppery, bronze, or dark purple (Figure 2).
FIGURE 2. Immature fruit of the common fig tree.
Ficus carica is a member of the Moraceae family (derived from the Latin name for the mulberry tree), which includes 53 genera and approximately 1400 species, of which about 850 belong to the genus Ficus (the Latin name for a fig tree). The term carica likely comes from the Latin word carricare (to load) to describe a tree loaded with figs. Family members include trees, shrubs, lianas, and herbs that usually contain laticifers with a milky latex.
Traditional Uses
For centuries, components of the fig tree have been used in herbal teas and pastes to treat ailments ranging from sore throats to diarrhea, though there is no evidence to support their efficacy.4 Ancient Indians and Egyptians used plants such as the common fig tree containing furocoumarins to induce hyperpigmentation in vitiligo.5
Phototoxic Components
The leaves and sap of the common fig tree contain psoralens, which are members of the furocoumarin group of chemical compounds and are the source of its phototoxicity. The fruit does not contain psoralens.6-9 The tree also produces proteolytic enzymes such as protease, amylase, ficin, triterpenoids, and lipodiastase that enhance its phototoxic effects.8 Exposure to UV light between 320 and 400 nm following contact with these phototoxic components triggers a reaction in the skin over the course of 1 to 3 days.5 The psoralens bind in epidermal cells, cross-link the DNA, and cause cell-membrane destruction, leading to edema and necrosis.10 The delay in symptoms may be attributed to the time needed to synthesize acute-phase reaction proteins such as tumor necrosis factor α and IL-1.11 In spring and summer months, an increased concentration of psoralens in the leaves and sap contribute to an increased incidence of phytophotodermatitis.9 Humidity and sweat also increase the percutaneous absorption of psoralens.12,13
Allergens
Fig trees produce a latex protein that can cause cross-reactive hypersensitivity reactions in those allergic to F benjamina latex and rubber latex.6 The latex proteins in fig trees can act as airborne respiratory allergens. Ingestion of figs can produce anaphylactic reactions in those sensitized to rubber latex and F benjamina latex.7 Other plant families associated with phototoxic reactions include Rutaceae (lemon, lime, bitter orange), Apiaceae (formerly Umbelliferae)(carrot, parsnip, parsley, dill, celery, hogweed), and Fabaceae (prairie turnip).