NHS Greater Glasgow & Clyde Area Drug and Therapeutics Committee
Greater Glasgow and Clyde Medicines
Medicines Update

Drug induced photosensitivity (July 2014)

At this time of year, with improving weather and the peak holiday period, the incidence of reactions to sun increase. Some medicines cause particular problems. Dr Paula E Beattie, Consultant Dermatologist at the Royal Hospital for Sick Children described some of the issues.


Drug photosensitivity reactions occur when a drug or metabolite within the skin interacts with ultraviolet (UV) radiation in sunlight. The drug may be ingested, injected or rarely applied topically. The vast majority of photosensitive reactions are phototoxic reactions.


The majority of drugs absorb UV wavelengths. A phototoxic reaction occurs when the drug present in the skin absorbs UV wavelengths specific to that chemical, becomes excited and produces a photochemical reaction which damages cellular components resulting in inflammation.


It can occur in any subject with sufficient exposure to the drug and to UV radiation; for example, doxycycline at a dose of 100mg will photosensitise 10-20% of individuals in Western Europe but at a dose of 200mg in summer months or in sunnier climates will photosensitise a much higher proportion.

Photosensitising Drugs


fluroquinolones, tetracyclines, sulphonamides




Thiazides, Furosemide


Amiodarone, Quinidine


Naproxen, Piroxicam

Ca channel blocker

Nifedipine, Benoxaprofen

Psychoactive agents

Phenothiazines, Chlorpromazine

Dermatology drugs

Psoralens, Retinoids

PDT agents       

Foscan, Photofrin







Various patterns of phototoxicity are recognised:

  • most manifest as an exaggerated sunburn reaction and so the diagnosis is often missed
  • recurrent immediate erythema (redness) can give way to a chronic exposed site dermatitis with drugs given long term, eg thiazides.
  • recurrent phototoxicity may sometimes be associated with photocarcinogenesis, eg vorioconazole. 
  • an immediate prickling, burning, erythema and swelling can also be seen, sometimes with delayed erythema and pigmentation. This pattern is most commonly seen after chlorpromazine and amiodarone (slate grey pigmentation)
  • exposed site telangiectasia can occur when calcium channel antagonists target blood vessels
  • increased skin fragility and blistering (pseudoporphyria) can occur with NSAID, tetracyclines, furosemide, amiodarone and fluroquinolones
  • photo-onycholysis, where the nail separates from the bed, can occur with doxycycline.


A small proportion of reactions may be attributed to mechanisms other than phototoxicity, see below. Many will cause a typical pattern of reaction but some may cause photosensitivity by more than one mechanism, eg phenothiazines.


Photosensitivity types

Drugs implicated






Lupus erythematosus











Photoallergy is a rare type IV hypersensitivity reaction which occurs most commonly with a topical chemical, eg sunscreen or NSAIDs, to form a photoallergen which presents as an exposed site dermatitis.


Knowledge of drug interaction with wavelength absorption can inform advice to patients on duration of photoprotection required. Potentially scheduling evening dosing of drugs such as flouroquinolones which have a short effect may help avoid phototoxicity. 


Advice to patients when prescribing a potentially phototoxic drug

  • Use photoprotection, including clothing and hats. Clothing should be of a fine weave so that light is not transmitted when held up to the light.
  • Avoid the sun between the hours of 11am and 3pm and seek shade when outdoors. Note that shade from trees and umbrellas is not total shade and that variable exposure still occurs. UVA can also be transmitted through glass.
  • Sunscreen should be very high factor. Most individuals apply it at a thickness that achieves a SPF 5-20 from an SPF50 sunscreen. Apply liberally and reapply frequently.
  • Sunscreens can be prescribed in primary care only for protection in abnormal cutaneous photosensitivity resulting from genetic disorders or photodermatoses including vitiligo, those resulting from radiotherapy; chronic or recurrent herpes labialis. The NHSGGC Preferred List option is Sunsense Ultra (SPF 50+).