Bergapten: has photosensitising properties and is often used in conjunction with solar radiation to treat psoriasis. Bergapten causes photosensitivity which is frequently used therapeutically against skin conditions like psoriasis and vitiligo where the patient is exposed to the sun as part of the treatment.

Use of bergapten on normal skin will also cause photosensitivity so exposure to solar radiation (the sun) must be avoided while using medications that contain this constituent.

Bergapten is a Linear Furanocoumarin.

Although it is generally held of all Furanocoumarins that they may be carcinogenic during exposure to the sun or other sources of UV light Bergapten is frequently mentioned as a potential photo carcinogenic, so please consult your medical practitioner before using substances that contain Bergapten.

Furanocoumarins: Furanocoumarins have sun- or photosensitizing properties and are often used for the treatment of skin conditions sometimes with controlled exposure to the sun.
Other effects of Furanocoumarins reportedly are: hypotensive activity, antiasmatic and antispasmodic.
Furanocoumarins are potentially photo-carcinogenic and may promote a cancer that is initiated by interference with the skins natural ability to protect underlying cells against the carcinogenic effect of harmful ultra violet radiation.
Furanocoumarins are Coumarins with a furan ring

Coumarins: Coumarins are lactones of hydroxycinnamic acids. Coumarins are lactones. There are many variations of coumarins: Furanocoumarins found in Angelica have a spasmolitic effect but must be used with caution as they have a strong phototoxic effect as has many of the Furanocoumarins (Warfarin a blood thinning drug but also virulent rat poison, is a coumarin derivative). In general coumarins have antifungal, hypotensive, anticoagulant and antimicrobial properties.
Many of the Coumarins are phototoxic and skin sensitising.

Lactones: A lactone is an Ester that's functional group has become part of a ring structure with carbon atoms.

Lactones are widely present in the plant kingdom and many are expectorants and febrifuges.