What do some drugs, cosmetics and perfumes with the sun have in common? Put together, they could cause you an annoying and painful rash: it is photosensitivitya skin reaction disproportionate to exposure to ultraviolet rays (in particular, grapes). It can be induced by several drugs, such as antibiotics and non -steroidal anti -inflammatory drugs (Fans), or by molecules present in creams and perfumes: they absorb energy from the UVs and download it attacking biological molecules and other cellular components causing damage to the skin. Photossensibility from drugs can take place with two different mechanisms: the photoxicitymore immediate, and the photoallergiawhich activates the immune system and is therefore delayed. The symptoms in the first case recall a solar erythema, with painblisters and swelling, while in the second case they are itching and desquamation. To prevent them, it is always essential to protect yourself using solar protection As a broad spectrum creams (UVA and UVB) and physical protections such as hats and opaque clothing.
Photosensitive, photosensitizing or photosensitization?
First of all, it is good to clarify some terminology. With the term skin photosensitivitymeans one abnormal and exaggerated skin reaction In response to the sun exposure, in particular to ultraviolet radiation (UV). It can be idiopathic, that is, the triggering cause is not known; linked to some pathologies such as lupus erythematosus; or caused by some substances. In that case we talk about chemical photosensitivity or photosensitization, and if caused by a drug we speak more specificly than Drug induced photossensitivity, DIP, A reaction induced by the interaction between drug and UV radiation, in particular grapes.
The term photosensitizing In fact, it refers to a substance that, ingested or contact with the skin, can interact with sunlight and cause a reaction of skin photosensitivity.
Photosensitivein addition to defining a person with high skin photosensitivity, it is also used to describe molecules that break or degrade if affected by solar radiation. It is good to clarify that a photosensitive molecule is not always, it is also photosensitizing: an example is vitamin C, which degrades if exposed to UV rays (therefore it is photosensitive), but does not damage the skin (it has no photosensitizing effect), indeed according to some studies it can help protect it from the harmful effects of ultraviolets.
The mechanism of action of photosensitivity and symptoms
Photossensibility from drugs can take place with two different mechanisms, the photoxicity and the photoallergiawho share the initial stage of the photosensitivity reaction (Solar light changes the pharmac moleculeor) then diverge in the pathological mechanism.
Photoxicity
The molecule absorbs energy from the UVs, finding itself in an excited state, called “hat -trick”. This situation, however, is not sustainable: in the stroke of hat -trick the molecule is energetically unstable And it must absolutely “let off steam”, releasing this accumulated energy: in order to return to its original state, the molecule gives heat, creates bonds or exchanges electrons and hydrogen. This leads to the formation of free oxygen radicals (ROS), as a superoxide anion, hydrogen peroxide, radical oxidrilic and individual oxygen that cause oxidivitiv stressOe attack cellular structures, from membrane to DNA. In reality, even the molecule in the excited state can attach cellular structures directlywithout involving Ros’s formation.
The symptoms are those of a solar erythema: blistersswelling, pain and an extensive erythema, which however affects Only the areas on displayfor example only the face, leaving the covered body parts of the body. It is a reaction rapidwhich appears within a few hours (from 30 minutes to 24 hours) from the exhibition and is dose-dependent: the more drug we took, the longer the exposure to UV, the more serious the reaction will be.
Photoallergia
Although more rare than photoxicity, it is also more subtle: the interaction with UV radiation changes the structure of the drug, making it a apthene capable of binding to skin proteins by forming a Photoantigne. This complex is recognized by the immune system and activates T lymphocytes: at a second exposure, the immune system recognizes the photoantigne as a “enemy” and attacks him, inducing a series of reactions that lead to skin inflammation.
The symptoms remember one more dermatitis with itching, desquamation of the skin and erythema, but appear only after the second exposure e they can appear on the whole bodyeven in covered areas.
What molecules can cause photosensitivity?
Drugs, substances contained in cosmetics, from the post -Abarbas to the perfumes to the creams: what unites these photosensitizing substances is the chemical structure. Often, in fact, they are polycyclic aromatic compoundsrich in heteroatomas (such as nitrogen and oxygen) inside cycles and halogen elements, such as chlorine, bromine or fluorine, and finally with groups capable of Attract electrons: In this way they can absorb the energy of UV radiation and “dribble” inside the molecule.
The list of photosensitizing substances is long and transversal and concerns both Topical products applied to the skin, which are taken orally. They range from antibiotics, in particular tetracyline, fluorochinoloni, non -steroidal anti -inflammatory (fans), such as ketoprofen e ibuprofen. Cardiological drugs such as some thiazidic diuretics and amoidarone or antidepressants such as chlorpromazine, sertraline and alprazolam, up to anticancer agents such as paclitaxel.
But the drugs are not the only ones to cause photosensitivity: to the appeal, substances present in cosmetics and perfumes must be added, such as Ossibenzone, the retinol And some of its derivatives, and the plants containing furocumarine, such as lime, celery and parsley.
Incidence and prevention of the DIP
The photosensitivity induced by drugs represents approx 8% of the adverse skin reactions unleashed by drugswith an increasing trend. According to some studies, this greater frequency is linked to aexcessive exposure to sunlight, without due precautions. However, it does not concern only the tan we take lying at the sea: all sources of UV radiation can cause photosensitization. So be careful also to solar beds, UV laser to diode and … your car! Well yes, chemical photosensitivity is more caused by grape rays, which they are not filtered by the glass of the machines or windows of our home, By making us exposed to the risks of chemical photosensitivity also inside the walls of the house or in our car.
Today, the security tests of a drug are also included photosensitization tests, according to the guidelines of both the European Medicinal Agency (EMA) and the Food and Drug Administration (FDA), to minimize the risk of related adverse reactions.
In our little one, it is fundamental Protect us with broad spectrum sunscreen or with physical screens such as hats or anti -UV clothing.
Sources:
