Photosensitization is the result of an interaction between ultraviolet rays (sunlight) and a sensitive substance in the skin. This sensitive substance could be a locally applied product (perfume, medicine) or a molecule delivered to the skin via blood circulation (photosensitizing drugs such as doxycycline or anti-hypertension medicines).
We can describe two types of reactions induced by sun:
- The first is an immediate reaction that occurs soon after the application of a product or taking of a medicine. Under the effects of UV rays, the skin reddens, as though sunburnt. It feels hot and painful. This is known as phototoxicity.
- In the second type of reaction, the substance in or on the skin is modified by the effect of sunlight, causing the body to recognise it as foreign. This causes a delayed itchy eczema-type reaction after 48 hours, which can extend beyond the exposed areas of skin. This is known as photoallergy.
Top tips if you are using a photosensitizing treatment
Dermatologists advise patients to avoid the sun as much as possible by staying indoors or in the shade. But if you do have to spend time outside, be sure to use a very high UVA-UVB protection product with at least SPF 50. Ensure all exposed areas of skin are covered, not forgetting the ears, nose, back of the neck, hands and feet.
When outside, wear protective clothing such as a wide-brimmed hat, long-sleeved t-shirt and long trousers. Photosensitizing drugs will not affect the sensitivity of your eyes but you are still recommended to use sunglasses in the sun. If your photosensitivity is caused by a fragrance rather than a medication, try applying it to your clothes rather than your skin to limit reactions. If you experience a photoallergy, you must stop the local treatment or the drug and consult a dermatologist.