2024-08-24 11:00:05
By Céline Couteau & Laurence Coiffard, University of Nantes
The “Do-it-Yourself” trend, which involves making everything yourself, can be more or less risky depending on the area concerned. When it comes to sun protection, the stakes are particularly high, since it involves limiting the risk of skin cancer.
By moving away from products developed by experts and relying on those developed by their peers, the consumer may feel that they are avoiding falling into the jaws of the industrial chemistry wolf, but in reality, they are exposing their skin to the fangs of the sun.
The evaluation of the composition and effectiveness of the formulas offered on the Internet reveals that they are generally not suitable for protection against ultraviolet rays.
We have recently tested 15 DIY sunscreen recipes available on the Internet. Three of the 15 recipes studied did not contain any sunscreen and therefore constituted a major risk for users in case of exposure to the sun. For the other 12, the sun protection factor was less than 6, the threshold value in Europe to be able to consider that a cosmetic falls into the category of sun protection products.
Recipes that lack precision and UV filters
On the Internet, many blogs run by individuals who do not have specific training in the cosmetic field offer homemade sunscreen formulas. research quickly allows you to find a large number of recipes for homemade sun products whose compositions are quite similar.
The “quali-quantitative” formulas are not extremely precise, the quantities being expressed in various units (g or ml), or reported to various utensils (tablespoons, droppers, etc.). Zinc oxide, used as a protective anti-UV filter, is thus present in the recipes at very variable concentrations (from 4.5 to 35%), some of which exceed the limit dose of usewhich is 25%.
Even worse: some blogs go so far as to offer homemade sunscreen formulas that do not contain any UV filters! Examples include the following mixtures:
– karanja oil, shea butter, coconut oil, carrot oil;
– shea butter, coconut oil, myrrh essential oil, carrot essential oil, lavender essential oil;
– coconut oil, shea butter, jojoba, sesame or sunflower oil, vitamin E, lavender, eucalyptus or rose essential oil peppermint.
Some of these ingredients appear to have been chosen based on an Indian study published in 2010Its authors, Chanchal Deep Kaur and Swarnlata Saraf, in fact attributed a high sun protection factor (or SPF) to different fatty substances and essential oils.
The problem is that the work of these researchers is based on an inappropriate protocol, based on samples in solution while usually the tests are done on solid support, and according to a different calculation method. Based on the Diffey and Robson methodour own work (currently being published) has not confirmed these results, far from it.
While Chanchal Deep Kaur and Swarnlata Saraf give coconut oil an SPF of 7.119, our tests determined an SPF of 1. Peppermint essential oil obtained an SPF of 6.668 for a dosage of 1% (1% essential oil for 99% excipient – in hydroalcoholic solution). This result would make it a super-powerful product, more efficient than the best UV filters on the market, since the latter provide an SPF of 20 for a dosage of 10% (i.e. 2 SPF units per percent)! However, our own measurements only give peppermint used pure, without dilution, an SPF of 1.
Let us also mention the case of theraspberry seed oilfashionable since researchers have attributed to it an elastic photoprotective power ranging from… 28 to 50 !
Unsurprisingly, fans of the Do-it-Yourself make this oil (as is, without any additions) a photoprotective product. A blogger living in the tropics even sees it as a “jackpot”, trusting only vegetable oils and essential oils to protect against UV rays. For their part, suppliers of cosmetic ingredients such as Oh Lou lou also praise the merits of this oil, “one of the rare miracles of nature that offers natural sun protection without destroying marine life like zinc oxide or titanium dioxide“.
However, work aimed at more rigorously re-evaluating the photoprotective powers of several vegetable oils has shown that the SPF of raspberry seed oil is much lower than that evaluated by the work cited above. The same observation on our side: the SPF obtained by us is 1.
Blurred view of SPF
Various sites whose names evoke medical advice also suggest saving money by using carrot seed oil or red raspberry seed oil to protect yourself from the sun. Elsewhere, zero waste enthusiasts suggest making an SPF 28+ sun oil (a statement that does not exist in terms of displayable SPF) made up of 30 ml of raspberry seed oil and 20 ml of coconut oil.
Bloggers who are more experienced in formulations multiply the fats in their recipes, but they mix the weights in grams, the teaspoons, the tablespoons, the drops of various oils and even whole mint leaves to obtain sun products whose SPF is determined… roughly!
Note that other voices are more nuanced: although mentioning an SPF of 28 to 50 for raspberry seed oil, they nevertheless recommend using this oil in the morning to moisturize the skin, and at night to repair and soothe it, adding that vegetable oils “are of course not sufficient to protect against intensive exposure to the sun.”
In fact, while some blogs are careful not to announce an SPF in relation to the proposed formula, others go the extra mile by recommending, for example, incorporating 5% zinc oxide to obtain an SPF of 2 to 5, 10% for an SPF of 6 to 11, and 20% for an SPF greater than 20… Not only are these SPFs indicated in a completely arbitrary manner, but it must also be remembered that in application of European recommendations, a product with an SPF lower than 6 cannot be described as a sun protection product.
Distrust of experts, trust in peers
According to Opinionway, the fashion of Do-it-Yourself is linked to the desire to save money: being prepared with everyday products, homemade cosmetics are supposed to be less expensive than industrial products. This fashion also reflects a distrust of experts and, on the contrary, a trust in one’s peers: entrepreneurs, hoping to ride this wave, also ask their community about the ingredients that should be included in the formula they are currently developing. It should be noted that by regularly pointing the finger at a certain number of UV filters, certain press titles can reinforce consumers’ distrust, even though this is not scientifically justified. This effect is further reinforced by the fact that various brands are riding this trend for marketing reasons, wrongly adding “free from” labels that can confuse the message for consumers.
The case of octocrylene illustrates this situation well. This effective UV filter has recently found itself in the spotlight, as a study has shown to degrade into benzophenonea carcinogenic compound, under certain conditions. In its opinion of March 31, 2021, the Scientific Committee on Consumer Safety (Committee scientist for Consumer Safety – an independent scientific committee that issues opinions on non-food substances on behalf of the European Union’s Directorate-General for Health) has stated that octocrylene remains safe to use when the maximum permitted doses are respected. However, various brands now use the words “octocrylene-free” on their products.
It should be noted that stating “octocrylene-free” when this substance is not prohibited may be considered as contravening European Union Regulation No. 655/2013 on claims (in other words, the communication elements that can be put forward by brands). Indeed, the text states in particular that: “Claims relating to cosmetic products must be objective and may not denigrate either the competition or ingredients used legally”. Furthermore, it should be noted that industrial products “without octocrylene” contain other UV filters whose behavior it is not always possible for scientists to assess, as they are protected by industrial secrecy.**
Let us recall in conclusion that in 2017, the National Agency for the Safety of Medicines and Health Products warned cosmetic manufacturers about their communication policy, emphasizing that a typical vegetable oil Karanja oil could not be considered a sunscreen product at all.
Beyond the advice to manufacturers, raising consumer awareness of the ineffectiveness of homemade sunscreens (and therefore the danger of using them) seems essential to us. For this reason, we regularly communicate on the subject on social networks. Because in cosmetics as in other areas, nothing beats the expertise of a professional!
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