Phototoxie (also phototoxicity) is a property of pharmaceutical and chemical substances. Describes the strength with which a substance under effects of sunlight on the skin surface causes poisoning (toxic ) effects. Modifies the sunlight is not the chemical structure of the substance, it is called photostable.


Active ingredients of drugs for the treatment of skin diseases (eg isotretinoin ) act phototoxic because their active ingredients are chemically altered by UVA and UVB radiation from sunlight.

The toxic effect manifests itself in different symptoms. The skin reacts mainly with redness, itching, dryness and flaking.

Some herbal remedies can act phototoxic at high concentration. Such a photosensitivity skin, for example, in patients who regularly use St John's wort preparations as an antidepressant, has been observed.

Causes of Phototoxie

Chemical bonds can be destroyed by high-energy UV-A radiation, inter alia, when the energy of the radiation is greater than the bond energy between the atoms of the substance. This can for comprehensive release of toxic or irritating substances from originally little / not come toxic substances. Also a chemical activation of the substances by supplying energy from the light is possible (eg warming). This can, for example, substances such as psoralen binding to the DNA molecules in the cell nucleus ( in the case of psoralen is a cycloaddition instead ) or cleave, whereby the cell may die or the immune system causes inflammation in the destruction of the ailing cell or to prevent the foreign matter, which also results in symptoms such as itching or rash result.

Phototoxic substances in everyday life

Furocoumarins that are common in umbelliferous plants such as giant hogweed (Giant Hogweed, Hogweed ), bergamot, angelica ( Angelica ) and occur in a number of other plants, as well as the fagopyrin of buckwheat (buckwheat disease) can cause phototoxic reactions.

Due to lack of knowledge about these plants, it always comes back to poisoning in people who have worked recently with the plants and have been in contact with their secretions.

List of phototoxic substances

  • Isotretinoin (such as Accutane)
  • Tetracyclines (eg, Vibramycin, minocycline, doxycycline )
  • Sulfonamides
  • Naphthodianthrone derivatives ( → buckwheat disease) fagopyrin
  • St. John's wort preparations