When the sun interacts with chemical molecules capable of sensitizing the skin, it is called " phototoxicity ". Unlike erythema and burns, caused mainly by short ultraviolet rays (UVB), toxic reactions are mainly due to the action of UVA. Some substances absorb the energy of solar radiation and transfer it to the skin tissues, causing damage to DNA or cell membranes.
The symptoms are the same as sunburn : redness, itching, swelling and burning, up to real burns with the appearance of bubbles. They can occur in areas where the topical medicine has been applied or, if the drug is taken orally or parenterally, they can affect all areas exposed to the sun. The dose of the drug and the frequency of treatment also make the difference. The reactions are more pronounced if the sun exposure has been intense or prolonged: they generally last a few days and can leave brown spots. The danger is greater if the exposure coincides with the peak concentration of the active ingredient in the blood. Among the most common drugs that can interact with the sun is: antibiotics (tetracyclines, quinolones and sulfonamides), oral contraceptives (pill), anti-inflammatories (especially those to be applied to the skin, such as ketoprofen gel / patches) and antihistamines (promethazine).
The so-called photoallergic reactions that only occur in predisposed individuals deserve a separate discussion, the symptoms do not appear immediately, but once sensitized they are also triggered by small doses of medication.
In any case, it is always a good idea to check the compatibility with sun exposure and always use adequate sun protection . If it is not possible to suspend or postpone the treatment, the sun must be avoided both during the drug intake and in the following two weeks.
