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Safety Concerns for Sunscreens

    Svetlya Anukudinova

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    Safety concerns arose in the past regarding the use of sunscreens containing organic sunscreens and nanosized physical sunscreens as well as products in aerosol form. The main scientific findings are summarized below;

    Organic Sunscreens
    One of the major concerns regarding the use of organic sunscreens is the possibility of skin penetration and as a consequence, potential toxic systemic effects. Due to their lipophilic nature, certain organic sunscreens could potentially penetrate the skin. Recent studies have, however, shown that although some sunscreens may be able to absorb into the skin, including the SC and viable epidermis, their level is far below the toxic level. Additionally, it has been shown that the data generated under in vitro conditions may overestimate in vivo skin concentrations of the sunscreen activities.

    Photostability of Organic Sunscreens
    An additional issue about many organic sunscreens is their photostability. As mentioned, the structure of UV filters may be negatively affected and or destructed upon UV exposure. Questions arose about whether photodegradation products can cause any short-term adverse reactions, such as skin irritation and allergic reactions, or long terms adverse reactions such as toxicity upon repeated exposure to these photodegradation products over months and years. 

    An additional concern is an increase in UV exposure due to degradation of the sunscreen, which could lead to sunburn in UV exposure due to degradation of the sunscreen, which could lead to sunburn and chronic skin damage such as skin cancer. 

    However, the reported occurrence of photoirradiation and photoallergic responses to sunscreens are rare compared with adverse events, such as skin irritation or sensitization, produced by cosmetics. Additionally, existing in vivo animal studies did not identify a health hazard related to the photodegradation of UV filters. Studies also showed that the long-term benefits of using sunscreens, protection against skin cancers, seem to outweigh any potential adverse consequences attributed to photodegradation.

    Sunscreens are thoroughly tested for efficacy as discussed, in both in vivo and in vitro studies. During these studies, sunscreens are exposed to UV radiation. Therefore, photo instability and photodegradation would become obvious during these studies if it was significant. Today's sunscreens containing potentially photostable UV filters always contain photostabilizing ingredients as well.

    Nanoparticles in Sunscreens
    RiO2 and ZnO are frequently used in sunscreens either alone or combination with each other as physical UV filters. Additionally, they are often combined with chemical filters since they can increase the efficacy of formulations.

    The main drawback of regular-sized materials is that they provide a white appearance when applied to the skin. This aesthetically negative effect, however, can be solved by decreasing the particle size under 100nm, which is referred to as the nano range. 

    Nanosized TiO2 and ZnO are transparent, which is cosmetically very appealing. However, concerns arose regarding the use of such small particles, questioning whether they can penetrate human skin and get to viable layers. Studies have shown that nanosized TiO2 and ZnO penetrate the upper layers of the SC only in healthy human skin and do not reach the living skin. Additionally, topical toxicity studies demonstrated that nanosized RiO2 and ZnO have low toxicity and are well tolerated on the skin.

    The weight of evidence suggests that nanosized physical sunscreens currently used in sunscreens (or cosmetic products) pose no risk to human skin or human health when applied topically. On the contrary, they provide a huge benefit by protecting human skin against the adverse effects of UV radiation, including skin cancer.

    Aerosol sunscreens
    The FDA recently requested more information on the safety and efficacy of spray sunscreens to have a better understanding of whether these products are similar in efficacy and safety to other dosage forms, such as lotions and creams. As sprays may be inhaled intentionally, it is important to see whether they would pose a risk to consumers.

    Interesting Facts
    A nanometer (nm) is 1000 times smaller than a micrometer and 1,000,000 times smaller than a millimeter. Nanosized materials cannot be seen with the naked eye. To give a better understanding of how small nanoparticles are, here is an example;

    the diameter of Caucasian hair varies from 50 to 90 micrometers, i.e., 50,000 to 90,000 nm. Just think about it; it is hard to see the width of a hair with the naked eye, without using a magnifying glass. Now you understand how tiny a nanometer is.