Photosensitivity

Human medicine

Main article: Photosensitivity in humans

Sensitivity of the skin to a light source can take various forms. People with particular skin types are more sensitive to sunburn. Particular medications make the skin more sensitive to sunlight; these include most of the tetracycline antibiotics, heart drugs amiodarone, and sulfonamides. Some dietary supplements, such as St. John's Wort, include photosensitivity as a possible side effect.

Particular conditions lead to increased light sensitivity. Patients with systemic lupus erythematosus experience skin symptoms after sunlight exposure; some types of porphyria are aggravated by sunlight. A rare hereditary condition xeroderma pigmentosum (a defect in DNA repair) is thought to increase the risk of UV-light-exposure-related cancer by increasing photosensitivity.

Veterinary medicine

Main article: Photosensitivity in animals

Photosensitivity occurs in multiple species including sheep, bovine, and horses. They are classified as primary if an ingested plant contains a photosensitive substance, like hypericin in St John's wort poisoning and ingestion of biserrula (Biserrula pelecinus) in sheep, or buckwheat plants (green or dried) in horses.

In hepatogenous photosensitization, the photosensitzing substance is phylloerythrin, a normal end-product of chlorophyll metabolism. It accumulates in the body because of liver damage, reacts with UV light on the skin, and leads to free radical formation. These free radicals damage the skin, leading to ulceration, necrosis, and sloughing. Non-pigmented skin is most commonly affected.

Notes

References

1. (1994). "Dorland's Illustrated Medical Dictionary". W. B. Saunders Company.
2. JH Epstein. (1999). "Phototoxicity and photoallergy". Seminars in Cutaneous Medicine and Surgery.
3. Quinn Jane C., Chen Yuchi, Hackney Belinda, Shoaib Tufail Muhammad, Weston Leslie A., Loukopoulos Panayiotis. (2018). ""Acute-onset high-morbidity primary photosensitisation in sheep associated with consumption of the Casbah and Mauro cultivars of the pasture legume biserrula", '". BMC Veterinary Research.
4. {{usurped
5. (1979). "Veterinary Medicine". Baillière Tindall.