structural:expansion
Phytochemicals and research

Some Citrus species contain significant amounts of the phytochemical class called furanocoumarins, a diverse family of naturally occurring organic chemical compounds. In humans, some (not all) of these chemical compounds act as strong photosensitizers when applied topically to the skin, while other furanocoumarins interact with medications when taken orally. The latter is called the "grapefruit juice effect", a common name for a related group of grapefruit-drug interactions.

Due to the photosensitizing effects of certain furanocoumarins, some Citrus species are known to cause phytophotodermatitis, a potentially severe skin inflammation resulting from contact with a light-sensitizing botanical agent followed by exposure to ultraviolet light. In Citrus species, the primary photosensitizing agent appears to be bergapten, a linear furanocoumarin derived from psoralen. This claim has been confirmed for lime and bergamot. In particular, bergamot essential oil has a higher concentration of bergapten (3000–3600 mg/kg) than any other Citrus -based essential oil.

In general, three Citrus ancestral species (pomelos, citrons, and papedas) synthesize relatively high quantities of furanocoumarins, whereas a fourth ancestral species (mandarins) is practically devoid of these compounds. Since the production of furanocoumarins in plants is believed to be heritable, the descendants of mandarins (such as sweet oranges, tangerines, and other small mandarin hybrids) are expected to have low quantities of furanocoumarins, whereas other hybrids (such as limes, grapefruit, and sour oranges) are expected to have relatively high quantities of these compounds.

In most Citrus species, the peel contains a greater diversity and a higher concentration of furanocoumarins than the pulp of the same fruit. An exception is bergamottin, a furanocoumarin implicated in grapefruit-drug interactions, which is more concentrated in the pulp of certain varieties of pomelo, grapefruit, and sour orange.

One review of preliminary research on diets indicated that consuming citrus fruits was associated with a 10% reduction of risk for developing breast cancer.